In the story you quoted about how you found extrinsic motivation from the gang of boys in your class to prove your worth, also shows how driven you were and kept yourself focused and motivated until you achieved what you set out to, and sounds like a great example of intrinsic motivation as well to me. Getting triggered by something outside of us to start working towards a goal is just one part, the other and I believe more important part is to keeping ourselves focused, not losing sight of the goal and constantly keeping working towards it. This is where some of us I feel are less privileged, including myself :D
For me, staying focused has always been a challenge. I'll briefly explain how my cycle of motivation usually goes; I find motivation in something, mostly extrinsic, I start working for it, I feel very ambitious about it and get a lot of expectations attached about my ability to do it, I expect the best from myself, the task starts getting either boring or harder, I start fearing that I might not be able to do it, I can't afford to not be good enough at it, I come up with good excuses or rationalizations to quit doing it, and soon enough I give up. (And all of this has always been an unconscious process for me, until recently when I got aware of it. Psychology helped a lot).
I'm not sure whether this is how motivation or self doubt works for others or not, but for me its very incapacitating. So to move forward, and to keep myself motivated, requires my inner most strength and a lot, A LOT of positive self talk, and constant reminders of the fact that I should not expect myself to be perfect, that it's okay to sometimes not be good enough or even fail, and that none of this is worth stop trying!
My friends, my people, and their validation and support also helps me stay focused and motivated :)