10 life lessons of adulthood that my 20-year-old self would never have understood

Unless you land a job with Google, on Wall Street, or you're lucky enough to make it on screen or pen a best-seller, you will gain wealth incrementally, and you probably won't save much for many years. The cost of living alone, especially if you have debts to pay off, is hard to cover with most salaries offered to junior level employees. Your 20s will likely be spent building up a career that will later be profitable, but don't count on a ballooning bank account any time soon.

Friendships have always been important to me, and I was fortunate enough to have met a great group of people in high school, college, and in my early years of work. There was a time, though, that I could not have counted the people I thought of as genuinely close friends on my fingers and toes and then some. Now, I'd say it's down to fingers and maybe a foot. Which is still a good crew, to be sure, but I'm shocked to realize it has been more than five years since I've had any contact with some people I once saw all the time. And never through a falling out; it just happens.

Sometimes, you will try your best to no avail, your hard work overlooked, taken for granted, or in the worst cases, taken away from you when someone else claims the credit. I've had bosses put their proverbial stamp on projects over which I toiled, and I've had work of which I was proud met with a perfunctory nod. And in many cases, the reward for your hardest work is merely that level of commitment and effort establishing a new baseline.

In college, I could stay up late boozing with friends and still make it to class in the morning. In my early 20s, I could leave work, hit the bars or a buddy's house, and still be at my desk on time every day of the week. But as responsibilities mounted, and as my body changed, the party lifestyle had to take a major step (or ten) back.

As you get older, your body becomes less efficient at processing alcohol, you need more sleep to recuperate from late nights (both the booze and simply the activity), and you will likely have more reasons to play it cool instead of going hard (AKA kids and a home to manage and a commute, and all the rest of it).

Prioritize things in your life carefully, because you will not have time for everything. If you have a beloved hobby, set aside time for that instead of Netflix. If you love to travel, plan your trips well in advance, because spur of the moment adventures are a young person's privilege. Each new phase of life, from work to marriage to family, means less free time. And time is the one thing you can never get back, so use it well.

For years, my metabolism was so fast I paid basically no attention to what I ate, calorie-wise. I'd try to have plenty of fresh fruit and vegetables and avoid fried foods, too much salt, and too much red meat, but if I was getting a sandwich, there was never a question as to foot-long vs. six-inch, as to the bowl of soup or the cup, or whether or not I'd have another slice.

Now, despite still running a few miles several days a week as I have for a decade, if I eat a few extra snacks here or there or indulge in an extra large dinner for a few nights, the weight shows up. To maintain more or less the same body I've had for years, I have to take concrete steps I never considered when I was 20.

At first, a new relationship is fun and exciting and feels effortless and light. But most of that fades. Not the fun, that should always be there, and there will always be exciting moments even when you know someone through and through, but for a relationship to be successful in the long term, it takes real work, patience, and sacrifice. And if you never experience those sensations in your relationship, you are probably not properly committed to it, or else you have a strangely pliant, selfless partner likely lacking much character.

You will be amazed by how quickly you turn 30. Then 35. And then beyond, but I can't speak to that yet. What I can say is that I clearly remember conversations I had when in my mid 20s in which I talked about someone who was over 30 as seeming notably older. And those conversations feel like they happened last week, not last decade.

No matter what you do, you will disappoint people in your life, and often those you love the most. This is partly true because we all make mistakes — we break a promise, tell a lie, say something hurtful, forget something important, and so on. From these mistakes come the opportunity for growth and improvement, so own them and move on.

In other cases, you are entirely in the right to disappoint people because you'll do so by following a path they wouldn't have chosen for you. If doing what you believe to be right lets someone else down, let them down gently and follow your course. You can't be all things to all people, after all. You can't even be all things to yourself.