Mean-spirited mediocrities, especially those with a smattering of learning, are the most likely to be opinionated. Only strong minds know how to correct their opinions and abandon a bad position.
When I was young, I was sure of many things; now there are only two things of which I am sure: one is, that I am a miserable sinner; and the other, that Christ is an all-sufficient Saviour. He is well-taught who learns these two lessons.