Enzo, are you by any chance writing without a detailed master plan? That's pantsing (writing by the seat of your pants), and while some people finish whole books that way, plenty get stuck, write themselves into a corner, or otherwise cannot finish.
If that's you, I strongly urge you to hold off on writing until you've got a master plan that's both complete and detailed. If you know how each scene or chapter stems from the previous one and leads to the next one, what happens in each chapter, who's there and where and when it's set, that's probably enough. A summary might run you ten or fifteen single-spaced pages, or you could outline or use a spreadsheet. Whatever planning method works for you is perfect, right?
Only when your plan is done to you let yourself start. As you write, you'll probably get some ideas that are even better. Stop to do two things: first, copy your existing master plan, then in the copy, make the changes. (This leaves you with every version of the plan you had, so if you decide to go back to a different version, you can.) Then use comments on the part you've already written to note what changes have to be made for the new ideas to be incorporated. (If they're simple, you can make them now, but you don't want to take a lot of time on this. Comments like Make Jane a widow. Give her three kids. go way faster than actually doing that.) Now write from the point where you got your new idea, using it.
Maryn, who needs a plan