- common sense
- a tolerance for pain
- willingness to do independent research
- willingness to admit mistakes
- ability to ignore general panic
Out of the above list I think willingness to admit mistakes is the hardest. Acting on a mistake is actually even harder as this typically involves selling a stock at significant loss.
Over the 20+ years of investing I have gradually got better at avoiding mistakes. It is extremely rare to find a bargain selling at open market. Low P/E and P/B are typically there for a reason (look for them!). Same with very high yeild.
Out of the all "great ideas" I have had over the years very few have been actually great. I think roughly equal amount (if not more) have been in the exact opposite category. So I tend to be sceptical with regards to any "great idea" that I come up with.
Mistakes do happen when inveting directly into individual stocks as opposed to picking a safe ETF tracking sensible idex.
That's why adequate diversification is paramount.