How exactly does enmity work in the lore?

[Fateborn]

So what about Nidhogg, Alexander, Carrier Craft, Sophia, quite a few of these are fairly "intelligent" or "crazed" to ignore enmity generated and yet does not acts on said thoughts, Alexander and Carrier Craft could just commune and conclude that the best course of action would be to eliminate the rear line due to their near-immunity toward hatred or tank's "getting in the way" attitude, while Nidhogg would be obviously blinded toward the humans and just destroy all around instead of focusing on that one puny being that happened to be apart from others, and Sophia as intelligent as she is (having lore wise planned to destroy Allag from the inside by allowing herself to be captured and releasing Primal Bahamut from its prison.) could chose to simply tip the scale so far down you FALL off instead of just enough that they "might fall off". So, yeah. Just a few of the examples.

[Jandor]

I think you have to think of the fights somewhat abstractly.
Enmity isn't just a representation of how angry things are with us, but also how well we're covering attacks, deflecting blows, etc. Nidhogg probably does go for the healer in "reality" but with high enough enmity we throw our shield Captain America style at his head and the fire he breathing ends up missing.
Every possibility would be a nightmare to implement though, so we have aggro bars instead .

[TinyRedLeaf]

I think you have to think of the fights somewhat abstractly. Enmity isn't just a representation of how angry things are with us, but also how well we're covering attacks, deflecting blows, etc.

Wow, abstraction! It's been a veeeeeery long time since I've seen anyone bring up this crucial point in explaining RPG concepts.

Long, long ago, back when table-top RPGs were cutting edge, and computer games amounted to no more than Lode Runner or Pong, there were players who asked a very pertinent question:

How is it that a Level 9 Fighter could have more hit points (9 hit dice, or 9d10, which ranges from 9 to 90 hit points, or a median of 50 hit points, before bonuses) than his sturdy, 4 hit dice heavy warhorse (ie, 4d8+12, or 16 to 44 hit points; median 30 hit points)?

Does this mean that a Fighter (of whatever race) is literally fitter than a horse? That he has more blood, meat and bones to lose than an actual horse, which could be up to 10 times more massive than a human?

Of course not!

It was explained that "hit points" are really no more than an abstraction of a number of real-life factors. For example, sheer size, and physical and mental stamina; the fighter's combat skill, which allows him to roll with the punches, and allow him avoid attacks that would have otherwise been fatal to less experienced warriors.

Hit points are also an amalgamation of a player-character's sheer will to live; a Level 9 Fighter could have sustained a multitude of blows, each of which would have logically killed a Level 1 mortal, but sheer willpower (as represented by his higher hit-points total) keeps him going.

For simplicity's sake, having more hit points just means any given character or NPC is harder to kill. But exactly how he is harder to kill is up to a player to imagine and role-play.

But in a time of increasingly graphic computer and video games — where every blow is literally represented on screen as a splatter of blood and gore — that aspect of imagination in RPGs has long since been forgotten. As a result, virtually all players today literally believe that a character with more HP has got a lot more blood to lose than the average Joe.

In short, having a gazillion HP doesn't literally mean a sneak attack, knife to the heart, which causes a mere 10HP in damage, wouldn't kill a player-character. It just means that, under normal combat circumstances, when the character is alert and ready, such a blow would have been deflected and result in no more than a mere flesh wound.

So, yes, enmity is a similar abstraction. Don't take it too literally. And if you really, really have to, use your imagination to rationalise how the noble paladin manages to keep insulting an elder dragon enough to keep the wyrm's focus.