You can wake up on a sunny morning, feeling better than you have in months. You can spend your morning classes in a pleasant peace. You can walk in the sun, hearing laughter, enjoying warm air on jacket-less skin, looking forward to enjoying the relaxing company of a good friend. You can, maybe for one of the first times in a pretty long while, be feeling almost ok about things, about your life, about what surrounds you, about the aches of the past and the unknowns of the future.

And in less than ten minutes, you can find yourself saying just about the worst thing that could possibly come out of your mouth. The meanest, coldest, bitterest thought that ever oozed along the sludgy bottom of your brain during your blackest moments somehow finds its way to your tongue.

And suddenly, you're back there, exposed, in all your full-blown ugly, and that wound, which seemed just about to start healing over, is ripped wide open all over again.

And then you're outside, damage done, wondering where the hell it all came from. And if you you'll ever be free of it. If you'll ever get to that place where it isn't there, lurking, waiting for even the tiniest trigger to force itself in, plough under all your good intentions, put the lie to all your efforts to "do the right thing" and have you thrashing and spitting, lashing out at the nearest loved one like a wounded animal.

The past does not cease to exist because we wish it away. We cannot simply chose the version of it we like best, seal it in memory like a time capsule, and move on. It remains. And as much as we'd like to think we can choose a moment to cut it off, and then manufacture our present and future into what we'd prefer them to be, we don't escape what has been.
Even to the degree that we may seem to succeed in making fate our slave, our past remains. It inhabits us in shadows and continuing threads. We react against it, reconstrue it moment by monent, we unknowingly mimic and repeat . But is there. We are what we are because it was.
We try to twist it to fit while it is busy twisting us.

That is to say, we are not, and will never be, fully "grown up".