Discipline
The ability to execute your trading plan without deviation, even when emotions scream at you to do something different.
Discipline is the consistent execution of a pre-defined plan regardless of how you feel in the moment. It is the single trait that separates traders who last from those who blow up.
Discipline breaks down in two directions: you skip a valid setup because you recently had a loss, or you take a trade outside your rules because a setup "feels" great. Both are discipline failures with the same root — emotional override of a logical process.
Build discipline structurally: checklists before every entry, maximum daily loss limits enforced by a broker stop, and a journal that makes every deviation visible. You cannot willpower your way to consistency; you have to engineer it.