There's hardly any equivalent to satisfaction achieved from completing difficult tasks. Satisfaction holds different meanings to different people; for me, it was, as strange as it sounds, beating a videogame boss. And not just any video game boss, I beat one of the toughest video game bosses of all time. I beat Malenia — Blade of Miquella, also known as the Goddess of Rot.
Caution, the article has gaming terms and references, but you can think of it as another 'I Did It' story; one I am super proud of since it took me a while to slay the Demigod.