You need to believe in something, but at the same time, you are going to be wrong a considerable number of times.
The balance between confidence and humility is best learned through extensive experience and mistakes.
There should be a respect for the person on the other side of the trade.
Always ask yourself: Why does he want to sell? What does he know that I don’t?
Finally, you have to be intellectually honest with yourself and others. In my judgment, all great traders are seekers of truth.