When fighting in Kumite, you must have confidence at all times.
Confidence develops from constant practice.
Overcome your flaws, sharpening your techniques in which after years of practice you will achieve a state where you can perform your best at all times. Your confidence will also come from having self-control and most important, a strong desire to win. Prepare yourself for the rules, a large audience, and for the referees so you can relax and face your opponent. This requires a strong mind which does not necessarily come with experience. It requires an ability to judge your opponent without mistake and by having faith in yourself.