When you presume a feeling for someone else, you're robbing them of their own agency.

You may not even be wrong, but people have a right to choose how they feel about something, how something affects them, and the only way to know is to talk to them about it.

Attributing to someone a feeling or thought they themselves did not actually have is among the worst things you can reasonably do to someone on a daily basis without interacting with them at all.

I worry people don't quite realize how harmful this behavior is, or how often people do it.

The solution, as always, is to communicate. Just speak, using words, to the person you're inventing thoughts and feelings for. Often you've successfully detected something (we are social creatures, after all), but rarely are you right on the specifics.