No matter how careful you are, no matter how much stress you place on yourself, no matter how many hours of practice, you will eventually screw up somewhere. You are imperfect, and will always be flawed.
If you travel with a map, you will go off course from time to time. Your writings will contain typos. During speeches, you will stammer, hesitate, and mispronounce words. You will irritate and fight with your family.
Everyone else on the planet is the same way. Even Superman has his kryptonite issues.
Is this knowledge pessimistic, dark, and depressing? No - it is liberating! You are human! Do your best, then learn to live with the results and forgive yourself and others.