I strongly believe oversizing positions (due to concentrated investing or leverage) is a bad idea for most investors. Few have the emotional requirements and skill needed to succeed at it. You need to have conviction when positions move against you and more importantly you need to be right. If you have the conviction and you're wrong, that's when you lose big. Mistakes will be made, it's inevitable. The important thing is to survive them and learn from them, and putting huge chunks of money in a small number of stocks is a good way to blow up. This was my biggest mistake personally. I got lucky and was able to exit at a profit but it was a harrowing ride with huge unrealized losses in the interim. It could've easily ended with those losses realized. Never doing that again (hopefully).
