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.
And that is because trading imitates life, during our life we take millions of decision which do not really change our lives and not much would have changed if we had chosen another option.
However there are a few decisions that can make our life take a turn for the better or for the worse, and trading is exactly the same, and those are the decisions which test our abilities as traders, and if at the time we break our own trading rules then it is likely that things are not going to turn right for us.
the decisions we make must be based on personal analysis so as to result in a decision to transact, so we must realize that the decision carries a risk, so that if a bad reality occurs it will not be a deep disappointment, but instead we can make it a lesson so that later we can fix it gradually, until finally we will have a wealth of knowledge in trading. therefore the key is basically we have to be patient to process