The concepts of my music come from all kinds of different places. I've made plenty of songs out of messing about with a sample or synth with no clear direction, and I've once made a song by exaggerating how I felt while I battled a cold. However, what makes me finish songs is attaching a theme to them. I'll try to get clear inspiration from somewhere, whether that is a series of reference tracks, a mood, a place, or even a whole story. For example, I made a liquid DnB song as a tribute to OPN's Replica, a french house song in which I invented my own old-school sample inspired by a Persian pop song, and a krushfunk song focused in achieving a stereotypical desert level vibe.
It doesn't happen reliably. I can't count on myself to finish every idea I have, but I can feel when an idea is great and I'll almost hyperfocus on it when inspiration strikes.