The key to success in so many fields is subtraction. My investment results improved significantly when I stopped doing all of the following.....

1) Checking the performance of my stocks/portfolio on a daily basis and worrying about share price movements

2) Paying attention to analyst reports, except those with a negative view on stocks I own

3) Paying attention to market forecasts, macro commentators and 99% of news (which is just noise)

4) Paying attention to tipsters

5) Paying attention to fads and hype

6) Paying attention to the benchmark, e.g. replicating benchmark positions to reduce tracking error

7) Caring what other people think and what they are investing in (unless it's an investor I admire and respect)

8) Caring what happens in the short term

9) Worrying about whether other people are making more money than me

10) Over-reacting to short-term events (Brexit, Trump, Covid etc.)

11) Seeking diversification for diversification's sake (20 stocks is fine, 50 is far too many for me)

12) Investing in countries I don't understand (e.g. China, Russia, Japan)

13) Investing in businesses I don't understand

14) Investing in businesses before I've done the work to understand them

15) Investing in bad businesses because they look 'cheap'

16) Investing in businesses where I have doubts over the management and/or culture

17) Buying shares or any other investment for a quick return

18) Trading regularly

19) Trying to predict or make sense of market movements

20) Trying to predict anything other than the long term (5-year+) outlook for the businesses I own

21) Taking myself too seriously - the world won't end if my investment returns are a few percentage points lower than I'd hoped for

What have I missed?