Discipline
Following your rules whether you feel like it or not. The one skill that separates profitable traders from everyone else.
Discipline is boring. Not entering when the setup is B-grade and you're bored. Sizing down after two losses. Closing the platform at max daily loss. Every 'I should have stuck to the plan' trade was a discipline lapse, not a bad strategy.
Related
Learn to actually use Discipline.
Definitions are the easy part. The free first five modules put this on a real chart and make you do the work. No card required.