Why does Withdraw not trigger an Attack of Opportunity?

Question

In D&D 3.5 the Withdraw action is defined as follows:

Withdrawing from melee combat is a full-round action. When you withdraw, you can move up to double your speed. The square you start out in is not considered threatened by any opponent you can see, and therefore visible enemies do not get attacks of opportunity against you when you move from that square.

What I don't get is that an Attack of Opportunity is basically a free attack by your enemy because for one reason or another you let your guard down by casting a spell, or firing a ranged weapon, etc., etc. Basically you're not fully engaged in defending yourself.

How does fleeing combat not cause an Attack of Opportunity since you're basically fleeing combat?

Answer 1

It's a full round action.

Think of it like this: You are using the move action to move away, while using your standard action to pay attention to your surroundings, to make sure that no one can take advantage of the situation.

You do not just run away and flee, you do not let your guard down. Instead, you retreat safely.

Answer 2

Why does Withdraw protect you?

You're giving up both actions and move speed in order to leave the area safely. Withdraw lets you move at double your speed, but running lets you move even faster than that. So if you're just trying to get away as quickly as possible, a run would be a better action, but you can't defend yourself while going at your top speed.

You're not just turning tail and fleeing as quickly as possible. This action is a guarded movement, with you able to not do a standard action. If you think about it that way, it makes sense.

Note: It still can provoke an attack of opportunity

Here's the important part again, just to make sure that things are clear on the rule:

The square you start out in is not considered threatened by any opponent you can see, and therefore visible enemies do not get attacks of opportunity against you when you move from that square.

Against an enemy with standard 5' reach, they only threaten one square around them. So when you move out of that square, the Withdraw action lets you not threaten that square, and there's no attack of opportunity.

If you're fighting something with multiple squares of reach (like a large creature), they threaten multiple squares. If you use withdraw and move out of a threatened square into another threatened square, moving out of that second square will provoke an attack of opportunity.

Answer 3

Mala & Tridus' answers are good and accurate, but to elaborate a bit more, look at it from the game designer's perspective: withdraw is an intermediate solution between a five-foot step ( which usually can temporarily counter an attack of opportunity for a single round, but not a readied action and doesn't take you out of harm's way) and a run action (which can usually take you out of harm's way completely at the cost of an AoO). Withdraw hits the intermediate point: it will remove you from both AoOs and readied attacks without an instant AoO, but you generally remain within charging distance of an adjacent attacker. As Tridus described, run actions are the willy-nilly flights that gets AoOed, and is usually the result of frightened and panicked conditions.