Most people react differently when they're under pressure. They tend to be more emotional or reactive. They tense up and judgement is often impaired. Many talented athletes can't cut it because they choke when the pressure's on. You could be a brilliant analyst but a lousy trader.
Consistency is far more important than brilliance.
Just strive for consistency in what you do and let go of the performance expectations. The last key to achieving mental mastery over the game is believing that you can actually do it. Everyone is capable of being a successful trader if they truly believe they can be. You must believe in the power of belief. If you're a recluse skeptic or self-doubter, begin by pretending to believe you can make it.