When I was playing Silver for the first time, way back in the day, I was walking as fast as I could trying to get to the next town and advance the plot, when I stumbled upon this weird pokemon named "Raikou". It looked cool and all, but I could totally just come back and catch it later, when the plot wasn't calling, right? So I pressed "Run"...
-_- If I had known that wandering legendaries were such a #$%#@ to pin down and gradually weaken...
So I thought, surely I would never make that mistake again. When I got Sapphire, I was completely determined that if I saw anything at all that looked like it could be a legendary, I would drop whatever I was doing and try to catch it. So I'm going through the game all determined, and I see this lame little fish pokemon, "feebas". It seems about the same as magikarp, which means it'll be fairly easy to catch, so I run and carry on, certain that I can always come back and catch lots of them later on with no trouble...