I am much happier when I have cold hard cash at the bank than when I am owning shares. The moment I buy shares, I watch my portfolio like a hawk. My happiness starts to depend on how the portfolio is doing. When the numbers go down, my happiness level drops. Vice versa. It becomes an obsession.

Instead of thinking about coding and other things that occupies my thoughts on a normal day, I start to think about markets when showering, sleeping, eating, driving etc. When I am investing in index funds, I don't experience such. That's why I only invest in index funds these days.