Toughness is a Tier 2 perk in Call of Duty: Black Ops II. It reduces the player's flinch when being shot by 75%, and also decreases the redness of the screen when injured, making the player more accurate when under fire. This is comparable to the Hardened perk from Call of Duty: Black Ops.
Toughness is highly recommended if the player participates in firefights often, more so if using a weapon that relies on accuracy, such as an assault rifle, as the reduced flinch might easily allow the player to kill the enemy player. In close range combat, it is not as much of use, as the flinch it helps prevent is not usually a factor up close.