Never worry about things you can not change. From what you ate last night, to that one thing you might have done differently that would have changed your life completely; it does not matter one bit.

I believe you need to experience something truly life altering to really, really understand what this means to the fullest extent possible. It is an easy idea to dismiss as simple common sense or obvious. If you are forced to confront this head on with some event that massively alters your life, this ethos takes on a whole different contextual meaning. I wish I could convey the true power of this in words. I see it as a major life lesson. NEVER worry about things you can not change.

Also, feeling stupid about some mistake is something to value, and not a reason to belittle yourself. Feeling stupid, like you would like to make a better choice, is a sign of growth, or at least the opportunity for growth. Always remember, truly stupid people never feel stupid.