Getting an ActionReplay for Pokémon Sapphire and going "what do these codes even mean???" kinda kicked off my career.
Randomly changing digits in the warp-codes to see where it would take me and eventually just learning hexadecimal and GBA internals. Had a whole notebook too.
What game has taught you the most?
By "taught", I mean anything: history, geopolitics, philosophy, or just generally aided in your self-development?