Secret Achievements (Concept)

Secret Achievements

CONCEPT

Most achievement systems allow developers to hide certain achievements, obscuring details about them until a player has earned the achievement.

Secret Achievements can be used for several reasons:

Story spoilers - An achievement named "Death of a Hero" will typically guarantee a major character dying somewhere in the story. By hiding the achievement, players looking at the list won't inadvertently spoil themselves on the plot.
Hide upcoming content - As online updating has become more common, developers will sometimes enter achievements into achievement systems in anticipation of an update. They then mark the relevant achievements as secret to hide details about what the update will bring.
Hide unlock conditions - Rather than preserving something within the game, some achievements are hidden to preserve the achievement's unlock conditions. This is often done to encourage players to try different ideas, or to collaborate in trying to unlock the achievement.
Simply unreasonable to obtain - Tangentially related to hiding unlock conditions, some games will hide achievement details because the developers consider them excessively unlikely achievements for anyone to unlock.