He must be a risk taker, he must accept anything that could happen to his investments. He must of course optimistic and willing to learn from mistakes
in investing. He must be humble and willing to listen to others idea. A good investor also has the ability to apply this idea,  when investing, respect the opinion of those around you. Above all, respect markets. The day you are too sure of the direction the markets will take is also the day you can celebrate Fool's Day.