E.g. an enemy coming out of cover at a different position than when they last popped out is cool, but working out that coming out of cover is just a bad idea and waiting in ambush would be more realistic and smarter, but lead to stalemates.
Heck, you hardly ever see even vaguely decent morale implementations ("hey you just effortlessly killed 80% of my unit, so I'll, um, charge you!!!").
Again, in EverQuest some enemies would run away and get help. In World of Warcraft they just mindlessly attack until dead. EverQuest's AIs (lame as they were) were simply too deadly for a truly mainstream MMO.