My dear dog, if by your will you mean what you really want to do...

Supposing you are taking a dog on a lead through a turnstile or past a post: You know what happens (apart from his usual ceremonies in passing a post!). He tries to go the wrong side and gets his lead [leash] looped round the post. You see that he can’t do it, and therefore pull him back. You pull him back because you want to enable him to go forward. He wants exactly the same thing—namely to go forward: for that very reason he resists your pull back, or, if he is an obedient dog, yields to it reluctantly as a matter of duty which seems to him to be quite in opposition to his own will: though in fact it is only by yielding to you that he will ever succeed in getting where he wants.

Now if the dog were a theologian he would regard his own will as a sin to which he was tempted, and therefore an evil: and he might go on to ask whether you understand and ‘contained’ his evil. If he did you could only reply ‘My dear dog, if by your will you mean what you really want to do, viz. to get forward along the road, I not only understand this desire but share it. Forward is exactly where I want you to go. If by your will, on the other hand, you mean your will to pull against the collar and try to force yourself forward in a direction which is no use—why I understand it of course: but just because I understand it (and the whole situation, which you don’t understand) I cannot possibly share it. In fact the more I sympathize with your real wish—that is, the wish to get on—the less can I sympathize (in the sense of ‘share’ or ‘agree with’) your resistance to the collar: for I see that this is actually rendering the attainment of your real wish impossible.’

Yours, Jack -- Letters of C S Lewis