I completed the regional pokedex in Sapphire. This was no small feat considering the absurdity required to get a Feebas and then evolve it. Naturally, Feebas and Milotic were the last two I needed. I spent so much time searching for that damn fish. One of my friends caught one without even meaning to and bred it for me.
Oh, there was A LOT of level grinding using an exp share and the elite four to level up things to evolve. By the time I was done, I had maxed out how much money you can carry.
I had been doing this because one of the Game Freak characters promised me "Something great!" for completing it. Motivated by this mystery item of wonder, I pressed on. When I saw that certificate, my heart sank and I vowed never to catch them all again.