We can't go back. Goddess help us, we can't. I think the hardest thing about being an adult is coming to terms with that-- coming to terms with the fact that, yes, you can do *anything* you choose, but you have to do it from where you stand. There is no room for regret, for 'if only,' for 'otherwise.'
Let those thieves in the door and before you know it, you'll be left empty-handed without time left for anything else.