There are a lot of factors that determine who succeeds in life and who doesn't. A wonderful family background is one, so also is having the right connections and also the right company of people around you, etc. Luck comes from the fact that it's not all these factors that we can control, and when we control the ones we can the ones we can't control can work against us and destroy our efforts. That's why a hard-working and diligent guy can be finding it hard to make progress in life and a loafer will be sitting on millions. There are factors that worked against the diligent guy and favoured the loafer. Only if we knew and could control all those factors could we 100% "make our own luck", like Harvey Dent.