What are the best theories that you have heard? The best theories that I have heard are: Austrian Economics It shows that free markets economies create the most wealth. That makes sense because the richest countries are capitalistic countries. And that the modern banking system creates economic crises. Evolutionary Psychology It makes a lot of sense. Myers–Briggs Type Indicator It show the different personality types. It is not scientific, but I have learned a lot from it. Like self-knowledge and understanding other people.