You are probably a human. There is only so much variation in behaviour, perception, and experience between humans, except for occasional outliers which we can recognise in advance. So your experience is presumably sampled from the typical range in the general population. Then a first-person example may be taken as a point estimate: until you have more data, assume the experience for most others is within some maximum distance from your own.
That rule, of course, breaks in many cases. (Many misleading applications are considered the typical mind fallacy.) Formulating the rule explicitly like this makes it clear when and why it breaks:
Unless you know you're weird, or that people differ a lot in the ways you care about, assume everyone is about the same as you, until you can learn otherwise.