I'm in my 30s, and I've completely changed my mind about 5 things since I was in my 20s

• I'm in my 30s, and over the past 10 years, I've completely changed my mind about several things.
• My views on friendship, family, and confronting conflict have evolved since I was in my 20s.
• Changing your mind about something doesn't mean that you were wrong — it means your circumstances have changed.

The other day, my 5-year-old son told my wife and me that he knows everything.

Usually we allow such declarations to pass without much mention, as arguing with a 5-year-old isn't fair given the decades of life experience the parent has in their corner. But as he had been rather testy for much of the past hour, I demurred and asked him a question I figured he'd flub.

"OK, who's the vice president?"

After a long pause, his face lit up, and he replied: "Pence!"

I have no idea where he picked up that bit of trivia, but needless to say he won that round.

What I do know is that as a young man, I, too, felt like I knew it all. As a teenager, I was on top of the world, filled with knowledge about all things political, literary, countercultural, you name it. In college, I had something to say about every topic, regardless of how much evidence I had to support it.

The older I've gotten and the more I've actually learned about life, the more I've come to realize that none of us really know more than the tip of the iceberg. And that's OK, as long as we accept it and are willing to keep learning and listening. I've also learned that it's perfectly all right to change your mind about things.

Read more:Raising kids doesn't come with a handbook — here are 30 mistakes every parent makes

Changing your mind about a given topic doesn't necessarily mean you were wrong before. Rather, it means that your circumstances have changed. Perhaps you have more knowledge about an issue now, and you see the matter differently. Maybe life events have opened your eyes regarding a subject you had little thought of before. Or maybe one day you realize that what you once valued is no longer of much importance to you, or that what you once took for granted is now precious.

Here are five things I would never have believed in my 20s that I fully accept in my 30s:

SEE ALSO: Raising kids doesn't come with a handbook — here are 30 mistakes every parent makes

It's OK to let friendships fade

I've been laughably lucky when it comes to friendships. I'm still close to a friend I've known since preschool, three from my elementary years, eight from high school, four from college, and several more from my early years in the workforce.

Beyond this core group of people, whom I'm sure I'll know until old age, for most of my 20s, I worked hard to establish and maintain new friendships, whether with coworkers, colleagues from other companies, friends of friends with whom I felt I clicked, and so on. And I held onto friendships from days past that had never been that deep, but instead existed only because of shared history.

Now well into my 30s, I've accepted the fact that you just can't be all things to all people. Now any friendship I feel fading, I gently allow to go.

If you feel like you're putting in all the effort, or if you notice you and your former friend simply don't contact each other anymore, it's usually best to accept the reality of the situation. I'll gladly strike things back up with old acquaintances, grabbing a beer or coffee and talking of times past, but I will no longer work to maintain a relationship just because it was once so.

Conflict is natural — and should be welcomed

I'm naturally averse to conflict. My default used to be avoiding argument when possible and keeping the disagreement as brief and contained as possible when not.

Rather than repairing issues — whether with friends, colleagues, family, or, of course, my wife — I often left things simmering beneath a veneer of resolution, and they were almost sure to burst forth again.

As I've grown older, I've realized that conflict is not only unavoidable but also should be welcomed when there is a genuine issue standing between two people. I always argue calmly and without attacking, no matter whom I'm dealing with. But these days I am comfortable enough in my own skin to engage in a genuine give and take that, unpleasant as it may be in the moment, leads to a genuine resolution and shelves the issues.

You can't do it all, and sometimes you have to prioritize what's important

When I was a younger man, I kept a packed schedule, often lining up plans back to back from morning to night.

A hike with my wife in the morning. Lunch with one friend. A writing session with another an hour later. A drink with a group next. A movie later. And so on.

When home for the holidays or for a vacation, I'd try to see everyone I knew, often spending more time driving around my hometown of Washington, DC, than spending quality time with friends or family. And when visiting a new city, I'd spend 15 minutes at 10 places rather than an hour at three or four, and would end up without any appreciable experience of the town.

Now, I've accepted that I have to prioritize a few things, rather than jam in everything.