True, you can be right 10% of the time and still make money, you can also be right 90% of the time and still lose money
A good link to use but you need a sufficient amount of backtesting to be confident.
http://www.automated-trading-system.com/resources/risk-of-ruin-and-drawdown-calculation-tool/
http://www.albionresearch.com/kelly/default.php
I am a very strong believer in probabilities since I have a math background which makes me comfortable with trading options. I strictly adhere to the risk of ruin formulas and it has not let me down. I actually never look at a chart when trading, I only look at option chains