This quote means that no matter how much you wish you had done something differently, or that you could take back a word you had said, or that you should have said something when you remained silent, it doesn't do any good. What happened, happened. You can't take it back, you can't make amends...you can't go back to that time/opportunity and use it better. What this means is that you can't waste your life. Don't sit atound, constantly misusing the oppurtunities that God has given you! Get out there and LIVE with NO regrets!!! otherwise you'll be living with the regret for the rest of your life :) I hope this helped you out! :) Goodluck!
