Quotes / Set Right What Once Went Wrong

Guy: Benjamin Franklin?
Franklin: Yes?
Guy: I bring a message from the future! I don't have much time.
Franklin: What is it?
Guy: The convention you're setting for electric charge is backward. The one left on glass by silk should be the negative charge.
(We were going to use the time machine to prevent the robot apocalypse, but the guy who built it was an electrical engineer.)note 
xkcd #567: Urgent Mission

"We travel through time to help history along - give it a push where it's needed. When the Omni's red, it means history's wrong. Our job is to get everything back on track."
Voyagers! Opening

"One more ship will make no difference in the here and now. But twenty-two years ago, one ship could have stopped this war before it started."
Star Trek: The Next Generation, "Yesterday's Enterprise"

"Is it just the chance to get off the dreary Voyager sets for somewhere that looks a bit more dynamic, or is just the little boy in me that wants to go exploring? If I were going to request any assignment on a Starship I wouldn’t want to be stuck somewhere dull like under Picard’s care or in Janeway’s Starfleet hell, I wouldn’t even want to shack up with Annorax ("Year of Hell") and blast away entire civilisations. Nope, the Dauntless would be my ideal assignment, travelling backwards and forwards in time dealing temporal incursions. Frankly it’s a notion that has so much potential I’m surprised they didn’t pick it up as a possible candidate as the next Star Trek series rather than Enterprise. Just think of the possibilities, the cameos that could be had, the imaginative stories you could explore – a series with time travel built into its core can be quite malleable I hear (or at least a 50 year old British SF show tells me)."
Doc Oho on Star Trek: Voyager, "Relativity"

Past Charles Xavier: So this is what becomes of us? Eric was right. Humanity does this to us...
Future Charles Xavier: Not if we show them a better path.
Past Charles Xavier: You still believe?
Future Charles Xavier: Just because someone stumbles, loses their way, it doesn't mean they're lost forever. Sometimes we all need a little help.

(Richtofen just headshotted his future self)
Dempsey: Dammit Richtofen! I thought we were done with this!
Richtofen: What can I say Dempsey? Things change.
Nikolaï: Only a fool would dare to change history.
Richtofen: I am no fool, for what I do, I do only to secure a better tomorrow.
Dempsey: Well let's hope we get to see it.
Callof Duty Zombies, The Giant

"If all I have to do to survive is tweak the future a bit, what's stopping me? Oh, yeah, yeah, yeah, yeah, yeah. The ripple effect. Maybe it will mean that the universe will be ruled by cats or something, in the future. But the way I see it, even a ghastly future is better than no future at all."
The Doctor, Doctor Who, "Before the Flood"