- Misreading the Market: Probably the biggest real reason is that it's just plain hard to know what people will like. Worse, it changes all the time. What was innovative two years ago when you tried to Follow the Leader and greenlit the movie is now a tired old cliché nobody will see. Maybe you underestimated the audience… or overestimated them. The point is: sometimes even your best efforts fail.
- Bad word of mouth: The movie just happened to be so bad that people avoided it. Those who enjoy cheesy fun usually buy it on VHS/DVD, or simply pirate it later. The importance of this factor has only been increased by the Internet, which has drastically increased the speed at which word of mouth (good or bad) spreads, and led to the present day emphasis on opening weekends as an indicator of performance.
- Competition: This is particularly often in effect with summer blockbusters. People have a limited amount of brainless action they would watch, and if there's a lot of that available, some titles may be neglected. They also tend to be high-budget, and as such if the movie flops, it costs a lot. There is, however, often a principle similar to Award Snub in nature: several good movies (with similar target audiences) are released simultaneously, thus one of them performs truly spectacularly, another one flops, but both are considered great in hindsight (the hit E.T. the Extra-Terrestrial and the flop Blade Runner, for example).
- Poor marketing: Many a bomb became so despite (or due to) being an excellent movie in general. Incorrect or misleading information about them (or just plain lack of marketing) makes audiences rely exclusively on word-of-mouth, which is generally not enough for a movie to successfully perform. The internet has made this situation a bit better, but not that much. These movies almost always achieve cult status and can later become profitable on DVD.
- Other Circumstances: Sometimes movies flop due to something that's not directly related to the movie itself or the movie industry as a whole. For example, the first film to lose over a million dollars, Intolerance, came out at a time when its antiwar sentiments (which were widely held just months earlier) were going against the popular pro-war wave of late 1916. Funny Aneurysm Moments and Too Soon tend to hit disaster movies' sales very hard when bad timing happens; the September 11th attacks and the Indian Ocean tsunami, for example, killed a lot of those even though they were obviously filmed prior to the catastrophe. Maybe your headlining actor make a derogatory comment that leads to a boycott of the film. The same effect involves comedies lampooning airports, airlines, and the security process, which all brought down the film adaptation of Big Trouble, which was bumped to the Dump Months from its original position ten days after the 11th. Another example of unfortunate timing is if a movie's genre is killed prior to release.
Box Office Bomb
A Box Office Bomb (or less severely, a flop) is a movie for which production and marketing cost greatly exceeds its gross revenue, ergo fails to turn a profit for the studio behind the film. While in the press the two terms have some crossover, a flop may be applied to all disappointing results, but a bomb is outright failure costing studios millions. With today's budgets, you can even see losses in the hundred-million-dollar range. So how can you tell when a movie has bombed? This depends on several factors. First is how much the studio paid to make the movie, paying all those people and companies you see in the credits at the end, which is generally public information. How much the studio paid to promote the movie is also an important factor. The marketing budget is generally not public information but is generally a significant percentage of the film's overall cost. A $150-million production may well have had $75 million spent to advertise it. Put these together, and you can see that a movie mustn't merely cover its budget but probably needs to make twice that before it can begin paying for its marketing costs, much less become profitable. A common objection at this point is to bring up the international box office. After all, the film made several hundred million more then its budget around the world, clearly these studios just want us to think only America matters and the Hollywood press keeps buying it! Right? Well, actually… not really. Or not yet, anyways. While the rest of the world is a much bigger market and can rack up film returns in the billions, behind these numbers, overseas distribution is actually a lot less profitable for the studios themselves. Internationally, films will often see even less of a return than the domestic gross and may have additional costs like needing a local dub track. How much can vary depending on the country in question. So studios still count on covering their costs domestically and judge a movie accordingly. While it's possible in practice, aversions tend to be from marginal cases. Around the world, taste in American movies tends to favor the same films, and the biggest hits at home are also the biggest hits around the world. Good further reading on how much movies need to make can be found here. Commonly cited possible reasons for box office failures: