->''"The perfect is the enemy of the good."''
--> -- '''Voltaire'''

!!! Also Called:
* Binary thinking
* Nirvana Fallacy

A subcategory of FalseDichotomy, the PerfectSolutionFallacy is arguing that a course of action is no good because it isn't ''perfect''. This essentially assumes the opposite of the GoldenMeanFallacy; rather than assuming the extremes cannot exist and the middle is correct, it assumes the middle cannot exist and a solution is either absolutely perfect or entirely without worth. This is then used to argue that the hypothetical perfect solution must be used, or that a solution is useless because some part of the problem will remain after it has been implemented.

-->Using reusable bags instead of paper or plastic will help the environment.
-->However, using them won't solve the problem completely.
--> Therefore, since it isn't the best possible single solution, it isn't worth doing at all.

Since outside of mathematics a perfect solution to ''anything'' is unlikely in the extreme, this fallacy is usually combined with BeggingTheQuestion; a debater will assume a "perfect" solution is one which fits his argument and views ideally, regardless of whether his opponent would view the result as perfect or even desirable. Alternatively, it can be used to defend the status quo by counting up the flaws in a proposed alternative without comparing it to the current solution, which has its own flaws.

This is often the basis of an AppealToIgnorance; the claim then is that because we don't ''perfectly'' understand something, our theories about it are necessarily false.

There is a flip side to this fallacy. Some people will believe that their solution is perfect, and will defend it at all costs.

This fallacy is the basis of the proverbial admonition, "Don't let the perfect be the enemy of the good."

!!! Examples:
* Thereís that old saying: if a thing is not worth being well done, then itís not worth being done at all. Which itself is an inversion of an older saying that [[DefiedTrope defies this trope]] - "If a thing's worth doing, it's worth doing well".
* The ultimate example is rejecting anything you feel like on the basis that it has been imperfectly proven; for example, rejecting the existence of China on the basis that you have never seen it[[note]]Or if you have seen it, rejecting the certainty that your own memories aren't lying to you, or if you are seeing it right now, rejecting the certainty that what you're seeing reflects some external reality[[/note]]. This inevitably results in a philosophical concept called UsefulNotes/{{solipsism}} since it is impossible to prove beyond all ''possible'' doubt anything barring your own mind.
* This is popular when answering a technical question on the internet: "There is no solution to your problem which I can guarantee to work in 100% of all cases. So I'm not going to bother telling you what will work in 99% of all cases."
** Also common is ignoring the stated problem on the grounds that the questioner has in his or her ignorance already failed to follow a "perfect" approach or methodology and should never have come upon that question in the first place. In other words: "I won't give you the solution you're asking for, because the knowledge would clutter your mind. You should instead try to solve this problem, which will allow a more perfect solution." Especially annoying as while the odds are good responses of this type ''will'' satisfy the original questioner's needs and thus end the dialogue, there's bound to be somebody ''else'' who's already familiar with the issues, genuinely ''does'' need an answer to the question, and now has unhelpful nonanswers cluttering the search space.
* You will hear this combined with Poisoning the Well if you hang around a review site for any length of time; always in defence of something the poster likes that scored poorly. "Well, reviewer A might say that about game Z, but reviewer A scored game Y too high / low, [[HePannedItNowHeSucks so obviously this site is not trustworthy.]]" The implication is that because the site's reviews are not perfect, they are worthless.
* People who attempt to scare people into abstaining from sex often use this fallacy, with the argument that, since condoms don't prevent pregnancy and [=STDs=] ''100% of the time'',[[note]]whether by fault of the material or misapplication by the user,[[/note]] they are useless; never mind that they do so over 98% of the time. The "perfect" solution of abstinence is also BeggingTheQuestion, since the argument assumes everyone who ''intends'' to be abstinent at one time will ''continue'' to have sufficient determination to be so. Sadly, this fallacy causes some people to believe using condoms is a worthless effort and don't use them because they don't see the benefit.
* Used often by anti-vaccinationists. Their reasoning: a particular measles vaccine only protects 95% of the time, so they'd rather take their chances with a potentially fatal disease. In addition to being an instance of this fallacy, this reasoning also ignores that, due to [[http://en.wikipedia.org/wiki/Herd_immunity herd immunity]], 95% of the time is more than enough.
** Likewise, in many cases the anti-vaccine group uses the potential for side effects to argue against vaccines in their entirety, often failing to do a cost-benefit analysis for the vaccines. For example, the smallpox vaccine carries a very real risk, as it is composed of a live virus (the cowpox virus). If one chooses to vaccinate a country with the smallpox vaccine, some people will get sick with cowpox. However, when the world began vaccinating against smallpox, an estimated two million deaths per year were due to smallpox, with many of the remaining cases becoming disfigured. [[http://www.aafp.org/afp/2003/0901/p889.html This link summarizes the costs of vaccination (warning: graphic images of disease state).]] The world chose eradication, knowing some people would be adversely affected by the vaccine, over the millions more who would die terribly from smallpox. Furthermore, because of the vaccine, smallpox was ''eradicated'' in 1979; the vaccine would be irrelevant today if it weren't that some nations may attempt to weaponize the virus.
** Penn and Teller explain this fallacy and its relevance to vaccines for laypersons [[http://www.youtube.com/watch?v=RfdZTZQvuCo here]]. NSFW due to strong language, as expected from Penn and Teller.
** Opportunistic vendors of quack medicine use this fallacy all the time in the US. US law requires full disclosure of any and all side effects or known problems with any conventional, approved medical intervention. However, if a product makes no specific claims about treating a condition, symptom, or disease, then it is not bound to do so. As long as a product sticks to empty statements like, "Boosts your immune system!" and not specific, testable claims like, "Causes 95% of test subjects to develop Memory B cells capable of a rapid response on second exposure to Pathogen X!", the sellers of these products escape government oversight, regulation, and liability. These folks can point out the shortcomings of science-based medicine, but are under no obligation to provide scientific testing for their product and cannot be taken to task for failing to do so. Naturally, using this fallacy is in the marketing toolbox for these products.
* The responses to a single case of HIV being reported in the American porn industry. Dozens of activists screaming that the industry's voluntary testing system was worthless, because it had not prevented someone from contracting HIV in the first place. They ignored the fact that this system was what gave the porn industry an infection rate vastly, vastly lower than that of the general population. Though as the the above example, it also resulted in some members of the porn industry being shocked that the system was not 100% perfect.
* Among people opposed to welfare, it's used thus: "In spite of welfare, there are still poor people, therefore welfare doesn't work."
* This is often used by people who complain about the Tribunal in ''VideoGame/LeagueOfLegends''. "The Tribunal is supposed to punish trolls. There are still trolls in the game, therefore it doesn't work."
* This is often used by those who oppose animal testing. They cite the fact that animal testing isn't 100% perfect as a reason to do away with it altogether, even though we're still much better off with it than we'd be without it. (For the concerned, the law requires that researchers use non-animal analogs whenever they're available. Animal testing is only used when there is no other option.)
* Used in several episodes of Series/PennAndTellerBullshit. When discussing the American Disabilities Act, P&T take a man and his iron lung for a walk through town, noting several ADA-compliant shops and facilities that cannot accommodate him. No matter what accommodations a business implements, they state, somebody will always be left out, so why should the government be allowed to set and enforce an arbitrary standard?
* Discussed [[http://www.giantitp.com/comics/oots0490.html this strip]] of Webcomic/TheOrderOfTheStick, when Roy is getting evaluated by a daeva. The daeva says humans should just accept that they are not infallible and just try to be the best they can.
* In ''{{Irredeemable}}'' the FatalFlaw behind the Plutonian's FaceHeelTurn was the criticism he received from the population after all his acts of heroism. It is implied that he has a pathological desire to have everyone love him,and simply couldn't tolerate any criticism whatsoever, no matter how justified.
* An episode of ''Series/TheDailyShow'' lampooned a group of Fox News personalities who claimed that a proposed tax increase on the super-rich was worthless in eliminating the federal debt because it would generate "only" an additional $700 billion over 10 years, a small fraction of the overall debt. (Stewart and Co. then went on to show that raising taxes on the lowest-earning 50% of the population could only generate the same amount by claiming HALF of all of their material wealth in taxes.)
* This comes up all the time in politics, usually in the form of refusing to support certain candidates or laws because they don't completely solve our problems. It's a major cause of WeAreStrugglingTogether, as factions push for their perfect solutions.
* Commonly used to refute the reliability of [[TheWikiRule wikis]], usually TheOtherWiki. The fact that there's no way to permanently protect every single page from all [[WikiVandal vandalism]] or absolutely confirm that every last sentence added in good faith is absolutely true over all scenarios, becomes an excuse to claim the wiki is always wrong. When told [[Administrivia/RepairDontRespond You Could Always Edit It Yourself]], they claim disdain for cleaning up other people's messes.
* AndADietCoke is one PlayedForLaughs; while it won't make you lose a noticeable amount of weight, drinking diet soda ''does'' cut some empty calories and if you don't eat fast food too often, getting a diet drink or water the times you do isn't actually a bad idea. That's not even getting into the fact that nobody really thinks a Diet Coke will help them lose weight if they don't eat other healthy food.
* The UnpleasableFanbase phenomenon stems largely from this type of fallacy, as do Fan Dumb, Hatedom, Hate Dumb, etc. - basically, if the thing you like [[TheyChangedItNowItSucks changes even a slight bit]] and/or has so much as ''one'' flawed episode/book/issue/level/etc, it is RuinedForever, and [[FanHater nobody is permitted to like or enjoy things ever again]].
* As far as ''Fanfic/KnowledgeIsPower'' is concerned, the fact that Dumbledore's plan to defeat Voldemort had some flaws makes him as evil as Voldemort himself.
* Several instances of TooAwesomeToUse are generated by this sort of thinking: ''Even though I'm out of Potions and I don't have a healing spell, I can't use my Elixir now! I may be low on Hit Points but I've still got most of my Mana.''
* From Neil Gaiman's ''ComicBook/TheSandman'':
-->"They are using reason as a tool. Reason. [[ScienceIsBad It is no more reliable a tool than instinct, myth, or dream. But it has the potential to be far more dangerous, for them.]]"

!!! Looks like this fallacy but is not:
* Rejecting a solution which actually does ''prevent'' one agreed to be better from being implemented.
* Rejecting the presentation of something as an ''alternative'' to the current course of action when it is only actually suited as a ''complement'' to it; in this instance, the inability to provide 100% replacement means it cannot be regarded as an alternative. For example, "alternative" electrical sources are not capable of providing 100% of a country's energy needs, and therefore cannot be accurately described as an alternative to more conventional generating methods.
* Rejecting a solution because it has an unacceptable cost-to-benefit ratio.
** Rejecting a solution because of differing projected cost-benefit ratios, at least until the projections are agreed upon.
** Rejecting a solution because of different values to the costs and benefits, where one side values a particular cost or benefit more or less than the other.
** Asking if there is a solution with a better ratio. There is nothing wrong with wanting a perfect solution; but there is with rejecting a solution because it does not have guaranteed success.
* Pointing out that a choice didn't work as well as anticipated, ''after'' it's been implemented.
* Rejecting an argument or claim that something ''is'' perfect, due to a proven imperfection.
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