Thanks =)
It's psychological. The idea behind this is that a person wants to take their eyes away from their treasure so others wouldn't hunt for it too, something like this. And when you stare for a long time, it's like you imagine "Oh god I wish there were Ace of clubs and Jack of clubs instead of these 3 and 5".
By the way, the same thing usually works when you look at your hole cards for the first time. So whatever you have, you need to spend the same time looking at your cards before you fold or you raise with American Airlines.