Jejudo, South Korea
Roughly speaking this is an example of akrasia:
At a party, you offer me cigarette and I consider your offer. On the one hand, I reckon that smoking a cigarette now would be very enjoyable. On the other hand, I believe that smoking is detrimental to my health. Not only would smoking this cigarette be harmful in itself, I think, but it would also increase the probability of my picking up an abandoned habit of smoking. In short, accepting your offer for a cigarette decreases my chances of leading a long and healthy life. I consider this goal superior to that of enjoying the short-term pleasure to be gotten out of smoking. Given my own values and goals, as well as the extent to which, I believe, accepting your offer would interfere with or satisfy them, I judge that I ought to decline your offer. Next, I take the cigarette, muttering uncomfortably: "Just this once."
From "Akrasia and the Principle of Continence or What the Tortoise Would Say to Achilles", p. 381 in The Philosophy of Donald Davidson .
Reading Ron's comments, this event would seem to be, consciously and unconsciously, more or less fundamental to what human beings, more or less, do. I don't know how fundamental this point is, I don't know how fundamental Ron would takes this to be (At the very least, I think that when we follow reasoning such as this, he might say that it's probably more that a reasonable explanation coincides with our desires more than it decides what we desire.).
I suppose it doesn't say much for our self- proclaimed label: homo sapiens sapiens.
My difference, and I'm not sure how much of a difference it really is, is that those desires are always already affected by previous reasoning rather than being somehow pure and dominant all the time. I suspect we both agree the effects of talking yourself into something (As Golem does in the Two Towers.) has a minimal effect at best.
It takes time to do what we want, to train ourselves to do what we want.