evaluate

I don't say the right things or perhaps I start to examine, evaluate, compute

This stanza is about over thinking. Over thinking is such a nuisance. It is a huge distraction. It is like someone ringing the doorbell to the door to your brain all day long and they wont stop unless you answer the door. It can make you cause you to make mistakes because you think to far into the issue. In this case the narrator is over thinking what he is going to sat to impress a girl he really likes. I see this all the time at school and at home. Someone who thinks way to much about what they are going to say that they end up sounding sketchy.

I hear your point - overthinking is a nuisance, and yet we can understand the anxiety and insecurity that causes it. Very natural.