Definition
Synonym of count to ten.
Also Said As
How People Actually Use It
The fact that Valve (Game creators) can't count to three but can to 4,5,6 etc. popularized by the fact that the third Half-Life game wasn't Half-Life 3 but Half-Life 2:Episode 1
"John:Hey! Can't wait till Portal 3 comes out! Jack:Umm... Valve can't count to three, idiot. John: Oh! Then let's wait for Portal 2: The Sequel."
Source: Urban Dictionary