This Achievement is awarded for uncovering an easter egg that has shown up in multiple Halo games.
To unlock it:
From the main menu, select Multiplayer
Then select Custom Games
Select Halo: CE
Select any map
Click the right thumbstick to bring up the file save options
Enter ".fortune" as the file name (without the quotes, and note the period at the beginning)
A fortune/proverb will appear and the Achievement will pop.
You can do it multiple times to see different proverbs.
You can read more about this easter egg here:http://www.halopedia.org/.fortune
Here is a video by RandomChievo (not me):