People who no longer give a fuck, how did you achieve that mindset?

Here is a cliché long story that will never see the light of day:

Ever since I started having social interactions with my peers I wanted to impress them all, be loved and respected and be the "top dog". It was probably my desperation that made everyone avoid me during those years I still gave a shit.
In kindergarden I wanted to be class president just so I can win over my crush, but she liked this other guy. I spent my kindergarden days with 2 friends ( who I still keep in touch to this day), but I was mostly lonely.
Primary/middle school I had the same mindset, I desperately wanted to have a bunch of friends , win over my crush etc etc.
Whatever I did was seemingly unimportant and I got mocked for it.
Mocking evolved into severe bullying, and I spent most of my days in middle school either getting the shit kicked out of me or beating up someone who made fun of me.
I was a chubby loner at the time so I was an easy target for group bullying.
It was almost exclusively a group of people either physically or psychologically bullying me.

Well at the end of middle school I hatched a plan, I was gonna be the the "chad" in high school.
Most of my bullies were going to a different school, and any stains on my reputation would be cleaned up.
Mind you, I was a skinny fat kid about 163-4 cm tall and I weighed about 65 kg.
First year of high school I acted like how I thought a cool kid would act.
I hung out with the "cool kids", who mostly used me as the butt of the joke.
By the end of the year I got backstabbed by everyone who I thought was my friend, my crush at the time embarrassed me in the most spectacular fashion and some kind of disturbing pictures of my sister were circulating among my peers (not nudes or sexual content).
Basically I was ostracized all over again.
My grades were shit too because I thought If I acted like a rebel people would find me cool.
My gym teacher called me a "physical manifestation of disgrace" because I couldn't do 10 proper push ups, he almost failed me too lol.

That summer I had a severe identity crisis, I spent all of my life shaping myself to be someone who society would find appealing and in the process I lost even the tiniest fraction of self worth and character.
I was also angry at that gym teacher, I was angry at everyone and especially at myself.
So after a 3 day insomnia episode I decided to go for a run at 5 am (mind you I had never ran before in my life).
I ran laps until my legs gave out because of cramps. The next day I came to run again at 5 am. I started doing calisthenics as well.
Then by chance I ran into an old friend who was going through something similar. We started competing, who ran more, who did more push ups, who could do a single proper pull up.

Then after a while we started hitting the gym, naturally trying to outdo each other.
Then by chance we started training martial arts, again competing.

Then the school year started, I had almost flunked my freshman year so I decided to try extra hard this year. I guess studying was easy for me (who knew), by the end of the year I was the best student in my class (and probably the best male student in my generation).

By the start of senior year I grew 15 cm taller, added 23kg of lean mass and had a single digit body fat %. Things turned around and I was probably at a position to finally be "the chad", as most of my peers started to backtrack and trying to re-insert me into their circles or whatever. Girls (especially shallow girls) started to show me a lot of attention, I'd go as far to say I was sexually harassed by some of my horny classmates.

But at that point I discovered something, I no longer gave a single flying fuck.
I did not care about the opinion of anyone, not because I was seemingly at some kind of dominant position, but because I genuinely didn't need the approval of others. I knew who I was and I knew what I wanted to do.
I went on to study medical school, and that newfound confidence was tested, broken, regained and yada yada. I flunked here and there despite my best efforts.
But as time moved on, I started to filter out the voices of others more and more.
I'm at a point now where I really don't give a shit about society's expectations of what I'm supposed to be or do.
We are all going to die, nothing has an inherent meaning and there is no absolute truth.
The only thing that matters is your own voice and opinion of where you want to steer your life.

/r/AskReddit Thread