When we trade we look at expected return, risk/reward, profit factor, etc. But we rarely look at the emotional element. What if I made a bet with you for $100 and you had a 60% chance of winning, you would take it, right? What if it was for $1000? What about $10,000? $100,000? At what point does the possibility of losing a sum money, no matter how good the odds make a deal in your favor untenable? It isn't just the likelihood of loss, it is the ability to withstand that loss that needs to be taken into account.