[salesman]

I'd personally rather see something like Dusty suggested. A brief description of the challenge, or even just a name, would be better than telling players exactly what they need to do or not telling them anything at all.

For example, consider an achievement for winning 10 spars in a row. Instead of saying "win 10 spars in a row", I think it would better as "demonstrate extraordinary talent in the sparring arena" or something cheesy like that.

This way, you're still fulfilling the purpose of the achievement system (ultimately to get people to play by aiming for achievements) and not ruining the sense of accomplishment for the player. If you go 100% secret, you're losing the drive that having set goals will give a lot of players.