Two separate but related principles I've ingested over time (and maturity).
When I was about 16 or 17, I thought social lives were like snowballs. Or a Katamari Damacy game.
You roll around, collecting more and more friends, who remain part of your life forever. Until maybe death do you part.
Photo credit - GameSpy
But there's a factor detrimentally overlooked in that - change.
People's availabilities change, where they live changes, their priorities change. People change.
Everyone is changing all the time.
People I was really close with one year ago I don't talk to at all now.
Think of you and your friends like moving trains. The movement is change. You can be changing slowly or quickly, and in the same or opposite directions.
If you're not changing in compatible ways (the same direction) you'll eventually grow apart. Slowly or quickly.
Interestingly this doesn't mean you'll stop hanging out. Only if you're being honest with yourself and how you present yourself to the world.
If it feels like work to hang out with someone, I argue that you should severely limit your time spent with them. Why not a full stop? Well, it's up to you, but having someone different in your life can be of value too.
Also about 16 or 17, I believed there were many universal truths in this world. The reality is that there aren't.
Because everyone's different.
I'd read all this advice on the Internet and take it as absolute, universal truth. Being a teenager, most of this had to do with working out and talking to girls.
For diet and exercise, there are certain tidbits of information that will be effective for most people. But everyone's different.
Some people can eat carbs all day long and their body's response to carbs is minimal. My girlfriend is one of these people. For others, any amount of carbs and their body stores fat like crazy. Others still (me included) are in the middle.
A 5x5 weightlifting program might be effective for many people. For me, high rep ranges have always yielded better workouts. You'll only catch me at less than 10 reps hitting muscle failure.
And as for girl stuff, there are tons of articles saying "all girls think X" or "one little trick that'll have her X" ... yeah right.
No advice is universally applicable, nobody has all the truths. These are hard pills to swallow because we're all "seeking alpha." Maybe there's just not much of it outside of physics laws.
Paradoxically, this includes me. Follow at your own discretion.