Human beings are affected by conflicts of interest. Not weak minded people, not immature or stupid or unwise or careless people. People. All of them. It's how the heuristics in our evolved brains work.

I agree, if you have a view of people being rational actors, then Paul Graham seems like the kind of guy who would be able to rise above this kind of thing. We now know that this model of human behaviour is a fantasy. These types of biases affect your thoughts before they rise to conscious awareness.