A strange occurrence that is common in video games. It happens when you can't find something that you commonly see when you aren't looking for it. The effect is named after the 75th pokemon of the Kanto region Graveler and its tendancy to disappear when you look for it. This is surprisingly a very common effect.
Nerd 1: "I can't find my soul silver! It was right here all week!"
Nerd 2: "Its the Graveler effect."