Watch legendary hedge fund manager Paul Tudor Jones at work in the 1987 documentary, Trader.
See especially PTJ's comments on the importance of focusing on risk management in trading and investing (near the 33 minute mark):
"Where you want to be is always in control, never wishing, always trading. And always, first and foremost, protecting your ass.
...That's why most people lose money as traders or as individual investors because they're not focused on the money they have at risk. If everyone spent 90% of their time on that instead of on how much money they're going to make, they'd be incredibly successful as investors."
Related articles and posts:
1. Paul Tudor Jones and Peter Borish on trading - Finance Trends.
2. Paul Tudor Jones on trading macro - Finance Trends.
3. Sebastian Mallaby interview: future of hedge funds - Finance Trends.