Irrationality: What Is The Deal?

Today I did something that is a paradigm case of irrational behavior. I was in line at Starbucks, and although I wasn't exactly hungry, I wanted something. Along with my coffee I ordered a chocolate doughnut. I know from previous Starbucks adventures that those chocolate doughnuts are mm mm good.

I brought it back to my table, and I did some stuff on my computer, and I drank my coffee. The work I was doing was pretty absorbing, and I found myself sort of forgetting about my doughnut. After a little while had passed, I actually was hungry. I hate eating sugary sweets on an empty stomach; it always makes me feel kind of sick. What I really wanted then was a small, pre-workout, healthy snack. In the mall where my gym is there's a food court, and in the food court there's a sushi place that is super-convenient, and at the sushi place they sell these little snack-sized packs of nigiri. About $3.75 plus tax. They're kind of the perfect little snack.

I decided I'd wait, have a sushi snack, digest a bit, and then go to the gym. Now, the thing is, I don't know what the fuck I was thinking when I ordered the doughnut, because I'm trying to lose weight, and as I said, I wasn't even hungry.

So when I realized it was in my power to forgo the doughnut, the idea of giving it up grabbed me in a big way. So what did I do?

I threw it away. In the garbage.

If you were trying to come up with an example of someone who behaved irrationally, in the sense of being self-undermining, this is a textbook case.

So. What happened? Was it

1) I "changed my mind" twice: once when I went from "I'm watching my weight" to "I'll take that doughut" and once when I threw it away.

2) I suffered from "weakness of will" when I ordered the doughnut, and the will magically reappeared in time for me to throw the doughnut away.

3) I was never sufficiently committed to watching my weight, or to eating the doughnut.

I'm asking seriously. Socrates is famous for having thinking there is no such thing as 2) -- you always do as you just best at the moment, so the problem is with your judging not your asking.

Some other philosophers think 3) is right, but I've always had my doubts. I don't need full commitment to things to carry them out, do I? I mean, it wouldn't be better to be "wholehearted" about doughnut eating, would it?

I'm thinking maybe it's 1). And then, what I don't get is, how are you supposed to know when your changing your mind is going to lead you down the path of utter ridiculousness? Or isn't that something to worry about?