We had just talked about another child being "annoying." I suggested maybe it's because he really wanted to play with M and could sense that M didn't really want to play with him.

M:  Like I sensed that T didn't want to play with me.  But I just solved it out. That's what L should do.
Me:  That's true. But not everyone knows how to do that.  Even some grownups don't know how to do that.
M:  What??  But they have been on this earth for 45 years!  How could they not know how to do that?