Hard cap

Hard cap refers to a stat or other bonus that is capped at a maximum value. In Reaper of Souls and Diablo 3 version 2, the only hard capped stat is Movement Speed, which can only be increased a maximum of 25% from equipment and Paragon Points.

Hard caps are more common in other RPGs than in Diablo 3 and there were a number of hard capped stats and bonuses in Diablo 1 and Diablo 2.

During Reaper of Souls development the designers talked about implementing hard caps for some of the most popular stats, such as Critical hit Chance and Critical hit Damage, but elected ultimately not to include them.

Hard Cap Theorcrafting

There are two key benefits of hard caps. The first is to limit the power of characters to keep parts of the game viable or balanced. The 25% hard cap on movement speed in Diablo 3 is of that type, since players moving faster than that have almost nothing to fear since they can move so much faster than the enemies. Higher rates of movement speed are possible in Diablo 3, but they are temporary bonuses from skills or shrines or other such enhancements.

The other main purpose of a hard cap is to limit the value of a stat and encourage build diversity, generally as a sort of bandaid for game design that failed to make multiple values desirable. Diablo 2 used hard caps and break points to this purpose on resistances, attack speed, casting speed, and many more. A similar effect was often suggested by fans during Diablo 3 vanilla, where a number of key item few modifiers were vastly better than other modifiers, and players were thus always better off adding more Armor, or All Res, or Critical hit Chance.

If some of those bonuses had been hard capped (the theory goes) players would have geared to those caps and then diversified the rest of their gear, rather than always and only wanting a few modifiers, and always wanting as much of them as could possibly be obtained.