What is the best piece of advice another person gave to you?

I think that the best piece of advice that someone has ever given to me is to always believe in yourself. My family have been always repeating me this helpful rule. In my opinion this is something very important, but many people forget about this simple truth. I am rather a pessimist so before I make any decision I am always thinking about every bad thing that can happen. In my opinion when you are believing that everything will be alright that will probably happen, but every time I have to remind to myself this rule to calm down before stressful situation. My conclusion is that positive thinking with believing in yourself is the best way to have strength to pass every difficulty.