You might not know anything about them. In fact, there is a whole lot about each human that we can barely know anything about another one! For instance, people assume I play sports just because I am tall. One noteworthy example was that on the streets, someone kicked and tripped me, and I fell to the floor, yet I was blamed by a stranger a few seconds later for “scaring me” and “blocking the way”. I did not respond because I didn’t feel like arguing helped there, avoiding the fallacy that the world is just, because it's not.
Also see: Halo effect