For example, venti creme brulee lattes with whipped cream are bad for me. They contain dairy, which I react badly to, caffeine, which renders me strung out, and whipped cream, which renders me fat. Also sprinkles, sometimes. I know, logically, that they are bad for me and that I should not drink them. But they're also delicious.
And sometimes delicious wins. That's akrasia.
As an aspiring rationalist, I want to avoid akrasia as much as possible (that's why I have tea in front of me - that and holiday beverages being over of the year).
Since I like to have characters that represent a fair spread of humanity, there are some characters who are aspiring rationalists, too. They fall victim to akrasia infrequently, since they're specifically looking to avoid it, but they still do, since they're still aspiring rationalists. And, in my stories, they end up in extreme situations where their best interests might not always be clear, making akrasia nearly inescapable.
For non-rationalist characters, akrasia is much more frequent. They do things like go off on adventures to save the world, when staying where they are and filing a complaint with their local representative or calling the police would be more practical and be the more logical decision, as there are agencies which are more effective than they are as an individual and present lower risk to life and limb.
It's important to separate akrasia from the character judging outcomes using only the information they have, as opposed to information the author has. If the character has let their dog outside and hears a scratching at the door that sounds just like their dog, but the author has shown that it's a ravenous wolf scratching at the door, the character is acting in their best interest as far as they know when they let the wolf in. To a reader, it's achingly stupid, but the character is using the information they have available. To present the same character in a situation that really would involve akrasia, install a window next to the door. The character has heard stories on the news of wolf sightings in town. It's dark out, and the shape is canine, but distinctly not that of his dog. He wants it to be his dog, since otherwise it means something has happened to make his dog not send up an alarm. Does he keep the door closed and call animal control, or let hope rule and let in the wolf?
Take out the possibility of akrasia, and you as a writer remove a great deal of suspense from your writing. The three main conflicts are man against nature, man against man, and man against himself. A rationalist who acts always towards what is best for themselves removes the third conflict. An aspiring rationalist, however, may simply elucidate that conflict more than many.
In fiction, akrasia serves a purpose, and can be good. It adds conflict, and makes characters more relatable to we flawed mortals who don't choose rationally at all junctures. If the main character of Alexander behaved in a rational way, I'd never have made it past Chapter One with that particular story. This post is a result of more ruminating on the differences between good fiction and good life.
This post is also going up at my personal blog, Authors' Refuge, though at a later date because of the way buffer has fallen out.
And now, blog post complete, I shall go and drink something with sprinkles.