I learned this when I was a wee lad: I was playing Runescape and trying to solve a quest I was stuck on with a walkthrough. The guide said that the macguffin was on the first floor of some building, and I must have spent hours looking on the ground floor with no luck.
I finally asked my big brother for help and he said, "Have you tried looking upstairs?"
And there it was, blew my mind.
Dude, I had the same problem, but with a clue scroll! I cannot tell you how long I spent searching the bottom floor of buildings around the Ardougne square...