If Paul Graham realized that people can easily lose lots of money by investing, why did he devote himself to investing large amounts of his own money in high-risk businesses? I'm not being facetious, I just think that seems contradictory. If I had a lot of money and that same knowledge, I would invest very conservatively.
He warns that careless trading may lose money without setting off fear, he invests in companies he also guides them to try and help them succeed. He doesn't invest alone, the risk and decisions have other people he trusts watching or contributing. They turn down most of the applicants