Miss your cue on a movie set and the worst thing that can happen is that you end up on the bloopers reel in the DVD extras (unless you have a particularly harsh task-masker as director, in which case you could also face a stern telling off too).
But in wrestling, if you mess up, it's more often than not live - and even if it's not live in the sense of going out on TV as it happens, you're still being watched by thousands of unforgiving fans in the arena (many of whom are armed with camera phones to immortalise your mistake for ever after).
It's impossible to completely mask botches that alter the course of a wrestling match, but it is possible, some of the time, to at least improvise a new finish on the fly that sees the intended winner come out on top.
And, of course, some of the time it isn't. If it's a battle royal, for example, and someone who wasn't supposed to get eliminated ends up losing their footing on the apron, you're pretty much screwed (unless you're the accidental new champion left in the ring).