We had Charlie out cross-country skiing yesterday. Off leash, of course. Here, DH has just called him. Have you ever seen a dog who looks more eager to please than Charlie? More self-disciplined?

But: yesterday, Charlie ran out of self-discipline. With pretty horrifying results.

It was a progressive self-discipline breakdown.

Early during the ski, he tried to leave the golf course to check out a neighbouring property. They have dogs. Charlie wanted to snuff around, maybe leave a calling card. Or two. He looked at me, seeking permission. And a quiet word from me was enough. "Over here, Charlie. Stay with me." And he did.

Then there was a greater trial about halfway through our ski of some 4 km or so. One of the ponds is not completely frozen. There was a sole Canada goose swimming around, honking derisively. Canada geese are definitely wily enough -- and malicious enough -- to taunt a dog into the icy pond, swim him around to exhaustion, and watch him drown when he cannot clamber out. Charlie wanted to chase the goose. He tried to enter the pond from one angle. I told him "No, Charlie." And he obeyed. But he was ready to try from another angle. Just checking to see if I meant, "Not at all", or just "Not from the steep part of the bank." It took further negotiation, but he accepted it. My answer was, "Not at all." And he trotted away from the pond.

However, on the final uphill slope to the club house we encountered a temptation which proved completely overwhelming for Charlie. What was rippling the snow? A muskrat, far from the water, burrowing rapidly. Charlie saw it. He smelled it. He located the muskrat. He tossed it into the air repeatedly. And yes . . . he broke its neck. Not pretty. Gruesome, actually. Really upsetting.

It wasn't that Charlie was refusing to obey me. He simply did not hear me at all. I could not get his attention, no matter what. He had completely lost it.

We had to put Charlie on his leash, take our skis off, and wade up to our car through deep snow.

So: the point of all this? Charlie, no matter how angelic, is a dog. Yes he is. His hunting instinct is strong. It's true that in the summer he often sits on our verandah at home and watches the rabbits and would not think of chasing them, if we tell him to stay. But: the muskrat under the snow was just too intriguing. Just too much.

What all of this made me remember was a recent article I'd read about exhaustion of will-power or self-discipline. It's pretty generally accepted now that there are multiple kinds of intelligence. But apparently MRIs demonstrate that there is only one kind of self-discipline which "fires" one area of the brain, no matter what occasions the need for a particular instance of self-discipline. And if we wear out or use up our self-discipline (maybe biting our tongues rather than lashing back at an annoying child; or keeping cheerful when a client is rude and unappreciative; or enduring endless frustration in a long line-up at the grocery store: whatever) then we'll be much more vulnerable to "losing it" at the end of the day. Including, of course, in the food context.

That's why for me the most difficult time to avoid overeating is when I walk in the door after a long day at work.

That's why I have a big pot of soup waiting for me in the fridge, to heat up a bowlful in the microwave as quickly as possible. Rather than diving into the peanut butter, the cheese and the granola bars!! Rather than stopping on the way home and buying the kettle potato chips!!! (Yup, did that regularly when I weighed 230 pounds).

For Charlie, that muskrat was the equivalent of a bag of kettle potato chips. Large size. He'd simply used up all the self-discipline of which he is capable.

And: sometimes I do too. Sometimes I do!!