Word count always balloons in prose

I’m really bad at estimating how long my prose pieces are going to turn out to be. Both chapter numbers and word count. My “quick side fics” in Forever Captain, my Steve Rogers post-Endgame retirement series, always turn out at least twice as long as I expect them to be. I had a story that went so long I had to cut off the “prelude” part at 30k words. My current WIP The Hemingway Trip is eight chapters after starting from a proposed three.

It’s partially because I end up expanding, partially because things just take more space than I imagine. I believe a story should be whatever length it needs to be to fully be told, so I don’t really mind. But it means everything takes much longer to finish than I plan. And you’d think I’d have learned how to estimate better by now— but nope!