1) High fees
2) Reaching for yield
3) You (and your behaviour) are your own worst enemy
4) Mutual funds are inferior to ETFs
5) Asset allocation matters more than stock picking
6) Passive management is usually better than active management
7) Not understanding the long cycle
8) Cognitive errors are costly
9) Past performance is no guarantee of future results
10) Not getting what you pay for (advisers)

By Barry Ritholtz, whom I’m a big fan of. I pretty much start my day with his The Big Picture blog.