That Just Happened
That Just Happened is an achievement in Halo: Combat Evolved Anniversary that is awarded for completing The Library without dying on Heroic difficulty or higher.[1] It is represented by a skull on top of a purple octagon.
The Achievement is worth 10 Gamerpoints.
Trivia
The Achievement's name is a direct quote made by Marine NPCs in Halo 3: "Yeah, that just happened!"
Sources