It is misguided to think that the entire goal of life is to not mess up. Had that been the case, Hashem would not have bothered to create us, and He definitely wouldn’t have created challenges. Rather, the proper perspective is the positive: that our goal in life is to accomplish, and that self-control is one of the greatest acts we can do. By cashing in on this opportunity, you can become a great person, and having sinned doesn’t take that away. Greatness is in your hands! Remember that not too many people actually resist strong urges just because they know they should. Most people who appear unaffected by desire either don’t face it to a strong extent or actually give in to their desires in private.
If past sins that we no longer commit still gnaw at our conscience and make us feel down about ourselves, we must do a proper teshuva and move on. We must stop beating ourselves up, even if “that horrific sin” was our fault. Hashem created us knowing that we might make many bad mistakes. That is why He created teshuva. When you do teshuva, He forgives you and no longer holds your sin against you.
After repenting, we must no longer feel inferior for our wrongdoings. Instead, we should be proud that we admitted our mistakes and resolved not to repeat them. We should also take pride in the effort we invested to change despite the difficulty of kicking old habits. Past sins leave over powerful desires, and it takes constant vigilance to control them. This makes the accomplishment even greater.