By showing the jurors' difficulty to change their opinion about the defendant.
Juror #12 is a classic example of pride in that he is more concerned about his life and his reputation, his career to be involved with anyone other than himself. It does not matter to him if the defendant is guilty or not and he's too prideful to reverse his decision. The other example of pride is the old man not wanting to admit that he doesn't see as well as he would like. In fact, as it turns out, he is a very lonely old man wanting some attention.