Whatever you do they are there :) Why with a smile? Be positive! Everything that happens, happens for a reason and the main reason for any mistake to happen is to show to you: that's the wrong way to do things and it gives you an opportunity to find out the right one, to learn something you haven't thought about. I take every single mistake as an opportunity to improve.
No matter what happens to you in life is neutral. That you and only you who makes it positive or negative. Look always at positive side, learn and do better next time.
When you happened to make a mistake, calm down first. Panicking you won't find the right way to correct things. Take a deep breath and think objectively. Write down corrective actions and find those, you feel to be most effective. Remember, you are the key element and good thing is if the lesson with the mistake was effective enough, you won't repeat it again! ;)
Here come some positive things to look at: