Know the feeling when you think about what the other person (might) think of you and that affects how you feel about yourself?
And then you find out that the other person wasn't even thinking about you?
In our every day life, it is already a lot to just figure ourselves out, be alone also thinking about others AND what we assume they think about us. Additionally, our judgements are absolutely not accurate. Nothing against you, you might even be better than others (btw. we all think we are). However, there is just 0 chance you know everything about the other person's life, in terms of what happened and even less what's going on in them.
Maybe someone spilled coffee over them this morning and they are in a bad mood and not as empathetic or the other way, they just won the lottery but you will never find out, but sense their good mood, making them self absorbed for the day.
You get the idea, how tf should you know. Besides, keeping so many streams in your head just takes a lot of energy. Never assuming, if you feel sth is off, openly speaking about it and until then defaulting to sth good seems like a healthier way of dealing with things.
At least for me.