Fool me once, shame on you.This means basically, that you should learn immediately to not tap into the same trap a second time.
Fool me twice, shame on me.
A core message of my blog is that the first time something happens can be an accident, the second time you should start searching for the patterns to solve the problem and with the third time the problem could already be solved.
Everybody tells that making mistakes is normal. At least you should learn from it. - There are things you should learn immediately and there are things that need another happening to get the lesson. And other cases are "well documented" - so you should never suffer of those - learning from others that already failed.
Learning the life's lessons is essential. Whatever you experience, you should use it to improve your habits. Do not just try to improve, but dedicate a part of your time to learning from your experiences.
As quoted on the Positivity Blog in "Yoda's Top 3 Word of Wisdom": Do or do not... there is no try.
Related posts: Will to change is not enough, Find the root problem, The value of experience.