To quote Jeph Jacques:
Dora - "Maturity is knowing you were an idiot in the past."
Marten - "If that's true, then wisdom is knowing that you'll be an idiot in the future."
Faye - "And common sense is knowing you should try not to be an idiot NOW."
From this Questionable Content strip. Seriously, if you haven't read Questionable Content, you need to check it out!