Mitigation is a method of reducing the loss of health from physical attacks. The primary way of obtaining mitigation is through equipment with mitigation, generally called armor, that covers most of a character's body; another way would be through buffs. In order of effective mitigation given:
- Plate armor can usually be worn by Warriors, Crusaders and Clerics.
- Chain armor can usually be worn by Shamans, Rogues, Predators, Bards and the above.
- Leather armor can usually be worn by Druids, Brawlers and the above.
- Cloth armor can usually be worn by Sorcerers, Summoners, Enchanters and the above.
The tooltip on the Persona window states "You will absorb X% of the damage from a level Y opponent", Y being your current level. It is stated in the original manual that mitigation only affects physical damage, though that manual is extremely old. Resistances probably cover the mitigation of all non-physical damage.
Mitigation is a flat absorption; it never fails and never succeeds spectacularly, it reduces by a set percentage all physical damage that would otherwise lower your health. Avoidance is the alternate method of keeping your health, but avoidance has an element of luck which can be dangerous to rely on.
Increasing absorption% takes more mitigation points as absorption% gets higher, however, the survivability provided by one percent of absorbtion increases as absorbtion% gets higher.
How much mitigation is worth in terms of item value is debatable and flexible. The more health you have, the more mitigation will help you.