Inability to see that the perceived difficulty in using a system is due to your own mismatched mental-model/needs/scenario -- so inventing one which is overfit to your own needs/model at this specific moment, which fails to generalise and is eventually adapted overtime to more scenarios and becomes frustrating again.

The cause is lack of self-awareness.

I do the service alone in my free time. Documentation is my weak side, it takes time, desire and understanding of what should be there. I am from Russia and most of the users of the service are from Russia. This is the first time that so many non-Russian speaking users have signed up for ooko. Telegram has translation functionality, if anything.