Discipline is essential in Forex trading to stick to a trading plan and avoid making emotional, impulsive decisions. To train discipline, traders can establish a routine, set clear goals and rules, use a trading journal to track progress, and practice mindfulness and self-awareness. It's also important to maintain a healthy work-life balance and take breaks when needed to prevent burnout. By consistently practicing discipline and holding themselves accountable, traders can build the habits necessary for success in the Forex business.