Until you're too far in to go back but look down and realize you can't go forward either. Because you've messed this thing up so bad.
Painted yourself into a corner.
I'm not saying that I do this all the time, but I do this all the time. Worse, I don't have any good advice for preventing it. For me, most times, it'll present as a note from a beta reader -- or worse, an editor -- something like, "This doesn't make sense. Did you even read the first book in this series?"
Of course I didn't read it. I wrote it.
But upon being informed of whatever plot sin I'd engaged in, my job as a storyteller is to go back and make it work. If making changes in an unpublished book can tidy everything up, that's best, but if the violation is in a book that's already out on the market, I have to change what I can.
Sometimes, sad to say, this means I've had to give up some plot twists and reveals that I really, really loved. But I did it, and it's done, and no regrets, right?
Maybe the best advice is this: complete an entire series before you publish the first one.
No really. And stop laughing.