My dad once said "Remember, you can never lie your way out of trouble, you can only lie your way into more trouble." and I have found that to be true. If you want an up-to-date example, take a look at Peter Barlow in 'Corrie' - that just about sums up what my dad was talking about.
From both my mum and dad 'you can only do your best, and no one can expect more from you. Even if it doesn't turn out 100% in your favour, at least you can say that you gave it 110% and you'll necer look back and think what if I'd tried harder.' In other words, no regrets - at the time applying to GCSE exams, but many other things later in life too. Wish I could bottle my parents - make a fortune!
My dad once said "No matter how good you are at something, there's always going to be someone better and someone worse". I think he meant this to mean "The world is a big place" rather that in the depressing sense :).