Mistakes happen. They are part of life. My question to you is this: what do you do after your mistake? Do you use it to better yourself, help enlighten others or stay the same? I think that those are roughly the options you have.
To learn from a mistake, it can be small, medium or large. It doesn't have to be ground-breaking and earth-shattering to learn something. You can learn from even little mistakes and go "oh, I'll never do that again!" Or, your decision to never repeat something can occur after a lot of blood, sweat and tears and maybe someone getting upset and mad at you. I hope for the sake of argument, you have never made a mistake that big, but if you did, that you learned from it.
Staying the same and not moving on is often the easy choice. Learning can be more of a challenge. You can even learn from others mistakes, but that is harder to do. Many people have to go through the fire themselves in order to learn the lesson, or so they claim. I am one of those people who learn through doing, including mistakes. However, do some people use that as an excuse? They really, really, really want to do something that they know is wrong and everyone is telling them is wrong, but they just want to do it anyway because they know for the time being, it will be fun. They throw out this "I just need to see it's a mistake for myself and then I'll learn" line, but is it really an excuse to get away with something they know is wrong?
Borrowing a thought from a wonderful TV show, it's like smelling milk you know to be bad. Someone reaches into the fridge, smells the milk and gags, then turns around and holds it out to you, saying "here, smell this: it's awful!" Automatic response? You smell it of course. But why do we do that? We learn through doing.
Listen, even if you learn through doing, don't let that be your excuse to do something you know you shouldn't, I guess that's my bottom line. Listen to reason, listen to people who have gone before you and made the mistake before you. If someone advises you strongly against something and in your heart of hearts you know it's wrong, don't hide behind the "I have to learn for myself" shield because it's pretty thin and flimsy: you WILL get hurt, even if you don't feel it for awhile.