The audience I built for is the one I am in, and that made me worse at judging the product

I work all day in English. It is not my first language. Everything about the product comes from that: the rewriting, the translation, the part where you can speak a thought instead of typing it clearly.

Building for yourself is supposed to be an advantage, and mostly it is. You do not need research to know which moments hurt. But there is a cost nobody mentions, which is that you lose the ability to tell the difference between a real problem and your own habits.

A concrete example. I was certain the killer feature was rewriting, because that is the thing I personally do twenty times a day before hitting send. I built the whole pitch around outgoing writing for months. It took a stranger to point out that half my own feature list is about understanding things coming in, summarizing, clarifying, translating something someone sent me, and that for a lot of people that half is the reason they install it at all. I had underweighted it because reading in English stopped hurting me years ago. It still hurts other people.

So the product was right and my model of the product was wrong, and no amount of using it myself would have surfaced that. Only somebody else's confusion did.

If you build for yourself: what have you found that you were blind to precisely because you had already adapted to it?