I hate leaving a scene unfinished when I write. Whether it’s because I run out of time to write or because I am interrupted for long periods (as in until the next writing session), I find I can never truly pick it up where I left off. Most often, I have to return to the beginning of the scene and rewrite the whole thing. The mood I had when I wrote the first part of the scene is gone, so I find I can’t continue what I’d started. What was I thinking would happen? What did I find compelling at that moment. It’s been lost forever to me, so I lose the essence of the scene. Sometimes I will write a note or two to remind Future-Me what I had in mind, but not always—not often enough, unfortunately.
I think when you write as a “hobby” (I cringe to use that word, but what I mean is that I’m working a full-time job and writing in my spare quiet moments.), you don’t have the time it takes to write a long-form work. I started thinking I would write short stories, but the universes I had in mind wanted to swell beyond that format, so I took one “short story” and have run with it; now I’m over 6,000 words into it and the story is only just beginning to lift off, which seems pretty normal from novels I’ve read, some of which I had to give over 100 pages to truly kick off.
The biggest tip I can think of is to write down notes of how a scene will work if you don’t have time to finish it in the current writing session. It will help you gather your thoughts and even though your mood may change how it ends up finishing, you’ll still have the basic framework for your original intent.