I've always felt that people use close to 100% of their brain capacity. Some people just don't have any surplus mental energy to spare to learn anything complic

I've always felt that people use close to 100% of their brain capacity. Some people just don't have any surplus mental energy to spare to learn anything complicated; they would get angry and frustrated if they try; this emotional reaction is their brain telling them that it's too much. They do not have enough mental capacity for this and they will suffer negative mental consequences if they continue. Too much thinking can make some people crazy. IMO most people are hardwired to be irrational; it's their evolutionary strategy. Irrationality is bad for the system but it's generally good for the individual. You need an irrational mind to be able to come up with ideas which will resonate with the average (irrational) person.