The following is based on a real conversation that is taking place on at least one range somewhere in America even as I type this, guaranteed:
Shooter A: "Hey, dude, I noticed something about your reload. I learned this thing at this class that should shave a good half..."
Shooter B: "Piss off! Hardcore McFaceshooter* says there is no timer in a gunfight!"
Shooter A: "Oh, uh, hey, cool. You've taken a class from Hardcore McFaceshooter? I've been meaning to take one from him myself."
Shooter B: "Nah, I read where he said it on the internet."
But: Other than perhaps "Slow Is Smooth And Smooth Is Fast", no other single aphorism has been used to justify more mediocrity and lack of meaningful improvement by the unwitting than "There is no timer in a gunfight."
*Only partially tongue-in-cheek: I used that to distinguish from some trainers I've heard use that line that made me have to bite my tongue to keep from replying "How the #@%$ would you know what there was in a gunfight?" On the other hand, there are people in that thread who tell me that there isn't a timer in a gunfight, and I believe them, because they went and checked.