When I started getting pain in my wrists I assumed it was RSI from all the typing I did. Every other writer I know gets some RSI; why should I be any different? So I downloaded a few exercises for hands and wrists, bought some wrist supports and carried on. Some times the pain was not so bad, sometimes bad but nothing I couldn't live with.
Then I finished the first rough draft of the WIP and was having a major rethink about the structure which meant no writing. My wrists got worse, to the point of finding driving difficult, which was odd given I wasn't straining them by typing. Finally I went to the doctor who diagnosed....arthritis. Cue what feels like vast quantities of ibuprofen, cue pain free wrists. Cue also feeling a bit older than I did before, and a darn sight more stupid for making assumptions.
We make assumptions all the time. A writes faster than us, B writes better. C is more successful, D is making lots of money. It's all too easy to compare ourselves with others - but it's usually only what we assume is true of others. A boasts of a massive word count on Monday, and we assume it's true of Tuesday, Wednesday, Thursday and Friday and beat ourselves up because we don't write that fast. But maybe A is pleased because they've been blocked for the past couple of weeks. We don't know.
Comparisons are dangerous because many - most? all? - of them are based on assumptions. Like my wrists, we'd save ourselves a lot of pain and grief if we didn't make them.