It’s a muscle. It gets stronger when I flex, but it wastes pretty quickly as well. If I’m in the zone I tend to knock out 2000-4000 words a day that I’m fairly happy with. Any slower and I get bored and wander off. The last time I got bored was 2015 and I didn’t write for five years :’( It took a whole first draft of a novel to get back into it after that gap, and I’d hate to have to do that again.