The mind can proceed only so far upon what it knows and can prove. There comes a point where the mind takes a higher plane of knowledge, but can never prove how it got there. All great discoveries have involved such a leap
I have every sympathy for writers. It's a mystery to me what they do. I can edit. I can cross out and say, 'I'm not saying that' or, 'How about we move this to here? Wouldn't that make that bit of the story better?' But where any of it comes from is beyond me. I will never write a play or a novel.
A good athlete can enter a state of body-awareness in which the right stroke or the right movement happens by itself, effortlessly, without any interference of the conscious will. This is a paradigm for non-action: the purest and most effective form of action. The game plays the game; the poem writes the poem; we can't tell the dancer from the dance. It happens when we trust the intelligence of the universe in the same way that an athlete or a dancer trusts the superior intelligence of the body.
The best way is always to stop when you are going good and when you know what will happen next. If you do that every day when you are writing a novel you will never be stuck. That is the most valuable thing I can tell you so try to remember it.