Trying to win in the markets without a trading plan is like trying to build a house without blue prints – costly (and avoidable) mistakes are virtually inevitable. A trading plan simply requires a personal trading method with specific money management and trade entry rules.
Discipline was probably most frequent word used by the exceptional trades that I interviewed.
There are two reasons why discipline is critical. 

• Its a prerequisite for maintaining effective risk control.
• You need discipline to apply your methods without second guessing and choosing which trade to take.

A final word, remember that you are never immune to bad trading habits – the best you can do is to keep them latent. As soon as you get lazy or sloppy, they will return !