It has always been the "emotion" that has wrecked even the best of traders. Fear of loosing much and the greed of not wanting to take profit when supposed. Many traders have very perfect speculation of what the market is and the possible outcome but they prefer to violate their own rules by compromising when they see perfection has been achieved.
I believe that those you called best of traders have better knowledge on how to handle such thing as emotion. They know that the emotion is what takes them out of control and so they have to properly guide against it and a sure way to bring emotion down is to trade with low risk especially when the market is volatile. Another way is to understand the times of the market when it is ranging and highly volatile because of huge buy or sell. These times are such that a better trader is careful not to allow the emotion to have a better part of them.