In my experience people are often bad at explaining their inner emotions. Rationalisation is one of my favorite words!

I will often ask a friend why they acted a certain way, and I will carefully listen to what they say, but I often disagree with their stated motives - denial and lack of self-awareness are rife. This has nothing to do with people consciously trying to deceive me (there's another topic!). I have the same faults. I'm average at reading people, yet all too often I have to trust my own flawed instincts about what I think is going on.