"Let’s explore internal control, the key to trading success, from another perspective. When I’ve had discussions about what’s important to trading, three areas typically come up: psychology, money management (i.e., position sizing), and system development. Most people emphasize system development and deemphasize the other two topics. More sophisticated people suggest that all three aspects are important, but that psychology is the most important (about 60 percent), position sizing is the next most important (about 30 percent), and system development is the least important (about 10 percent). "
- Van Tharp