In the masterclass Ben Graham often emphasised psychology in his answers, as many of the best investors seem to do.

For example, ihe last question it was asked how effective dollar averaging. Most investors would go into the details of why is effective mathematically with fluctuating price, but Graham breezes past that and emphasises how errors of psychology completely dwarf the merits of the system itself - Graham answers as:

"I think there is no doubt, that if you put same amount of money in market year after one has a great chance of coming out ahead regardless of when he begins, and particularly regardless if he should begin now. You have to allow for the human nature factor, that no man can really say definitely know how he's going to behave over the next 10 to 20 years, and there is danger that people start with the idea of being systematic investors over the next 10 to 20 years, and may change their attitude as the market fluctuates. In the first instance, put more money into the market because they become speculators, and secondly get disgusted and scared and don't buy at all later on when prices get low. It's a psychological danger. The fault is not in the stars or in the system, but in ourselves".

The last sentence is especially succinct.