Many a times, our wasted chances are a result of a list of reasons we carry, tucked away deep in our heart. What if we could reason with our reasons and take that chance. Would it have turned out differently? The lesson I've learnt is to examine any decision I've got to make, and imagine if in 10 years, I would consider that to be a "thank God I did it" or "what if I would have done it".
Perhaps happiness is to contend with a lot less "what ifs" than we have on hand.