Post
The hidden scoreboard that determines which player the boss wants to murder the most.
Aggro (short for 'aggression') or threat is the system enemies use to decide who to attack. Every action -- dealing damage, healing, buffing -- generates a threat value. The player with the highest threat gets targeted. Tanks intentionally generate massive threat to keep bosses focused on them while DPS and healers stay safe. The system creates the classic MMO 'holy trinity' of tank, healer, DPS. Pull aggro as a healer and you're probably dead. Let the DPS rip too hard before the tank establishes threat and the whole pull falls apart.
Example
World of Warcraft's threat system defined the MMO genre. Classic WoW required DPS to watch threat meters like Omen religiously -- pull aggro on Ragnaros and you'd wipe the entire 40-person raid. Modern WoW simplified this, but the threat dance between tank and DPS is still the backbone of group content.
Why it matters
Threat systems create the role differentiation that makes MMO group content strategic rather than a DPS race. Understanding aggro is the difference between a smooth dungeon run and a wipe fest. For devs, threat systems are a powerful tool for creating meaningful team dynamics.
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