There are two types of rational beings, pure spirits and humans, which are a union of body and spirit.

Both are capable of making decisions that have consequences.

But humans are burdened with brains, a relatively inefficient muscle which limits^† how well our spirits can act. So we have trouble remembering things, we think pretty slowly, and we often forget things too. And we have to sleep all the time.

Spirits, on the other hand, don't have this trouble. They can instantly recall anything in their memory. They think with perfect clarity.

The flip side of this means all their decisions are final.

See, we change our minds all the time, like when we are able to think more clearly and realize we were wrong before, or when we remember something that changes the matter at hand. But spirits have no excuse. Their decisions are made with complete intent, full knowledge, perfect clarity.

To give a concrete example, when we will, or choose to grab that bottle of Pepsi, the message is first sent from the spirit to the brain, then the brain sends a signal down the spine to the limbs, and your arm moves and your torso turns slightly and you grab that sucker and down it. All this is possible because of our flesh, but all this is slow and inefficient because of our flesh.

Spirits on the other hand have nothing slowing them down. To will is to act. They don't act in the physical world since they have no physical bodies. But something as simple as choosing to defy the natural order is an immediate and permanent act.

Now, Satan is a spirit. So when Satan sinned, it was a final decision. There is no going back; in fact, he wouldn't want to.

^† it's usually less troublesome when doused with caffeine