As a kid, I didn't use the internet a lot, and I didn't know that it could be used for stuff other than homework. So every new Pokemon for me was worth treasuring, and I ended up spending about 700 hours in my Pearl copy, catching all Pokemon in Sinnoh. I did not know where to get Dialga, had no Pokemon-playing friend, nor had any GBA cartridge to make use of Pal Park, so except those, I caught a ton of Pokemon otherwise obtainable through wild encounters, excluding Legendaries (didn't know Arceus existed welp).
Other than that, I think it was in Black 2, I came close to completing the Pokedex, but haven't been interested since then.