I think the thing I will remember about my 20's more than anything is the crippling uncertainty about oh, everything. And I really hate uncertainty.
Once I graduated from college (and even in the months leading up to graduation), there was so much uncertainty that at times I was almost completely overwhelmed by it. Days went by where I couldn't make a single actual decision because so many things tied into other things that were also uncertain that I just wanted to put my head down on my desk and cry. I'd wake up, go to work, and try not to think about it. That was my main coping mechanism: denial. I'd concentrate on the things I could control (my sleep schedule, what shows were on the DVR, exercising, my weekend plans) and not think about all the other things that I could do nothing about (where I was going to live from year to year, grad school, my Life Plan, a career). For people who don't mind instability and ever-changing circumstances, living like this is ok, they can function just fine. For me, not so much.
I still struggle with uncertainty. People who are much wiser and often older tell me not to worry, that everything will work out ok, just relax and enjoy the ride. To this I say yes, I would love to, thank you, but it's not that easy. There's no switch that I can flip, nothing to make me change from who I am into who you are in one easy motion. To blithely tell me to do so is only sure to invite wrath, even if it's just in the form of a brow wrinkle and a mild "I don't really work that way."
So I understand that in the grand scheme of things, everything will probably work out ok, but that doesn't mean I'm not going to kind of freak out about it at points along the way. It's what I do.