Nothing causes akrasia. There is no such thing as akrasis. 'Akrasia' is the label you apply to a phenomenon you don't understand and you really need to think about more deeply.
It would probably help if you pointed out that the reason we have the illusion of akrasia is because people's built-in systems for modeling the intentions of other people, generate mistaken predictions about motivation and decisions when applied to one's self. It's sort of like looking at yourself in a funhouse mirror, and mistakenly believing you're fatter or thinner than you actually are.
In reality, it's not that you don't follow through on your will, it's that you've failed to understand (or even observe) how your behavior works in the first place, let alone how to change it. Most descriptions of akrasia and how to deal with it (including what I've read of Ainslie's so far), strike me as trying to explain how to steer a car from the back seat, by tying ropes to the front wheels, or by building elaborate walled roads to keep the car going in the right direction.
It makes me want to scream, "but you're not even looking at the dashboard or touching the controls!" Those things are not even IN the back seat.
They're looking for information in the human parts of the mind, while entirely ignoring the fact that the secrets of our behavior and decisions CAN'T be there, or animals couldn't live their entire lives without ever having a single rational, logical, or "economical" thought.
Thought is not the solution here, it's the problem. And the answers are in the FRONT seat -- in the mind-body connection. In emotions, and their somatic markers. In the internal sensory (not verbal!) representations of available choices and expected outcomes. All that equipment that was (evolutionarily) there LONG before the back-seat driver showed up and started critiquing which way the car is going.
And the back-seat driver is only confused because he thinks he's the one who's supposed to be driving... when he's really only there to wave out the window and yell at the other drivers.
And maybe persuade them... that he knows where he's going.
Akrasia is the tendency to act against your own long-term interests, and is a problem doubtless only too familiar to us all. In his book "Breakdown of Will", psychologist George C Ainslie sets out a theory of how akrasia arises and why we do the things we do to fight it. His extraordinary proposal takes insights given us by economics into how conflict is resolved and extends them to conflicts of different agencies within a single person, an approach he terms "picoeconomics". The foundation is a curious discovery from experiments on animals and people: the phenomenon of hyperbolic discounting.
We all instinctively assign a lower weight to a reward further in the future than one close at hand; this is "discounting the future". We don't just account for a slightly lower probability of recieving a more distant award, we value it at inherently less for being further away. It's been an active debate on overcomingbias.com whether such discounting can be rational at all. However, even if we allow that discounting can be rational, the way that we and other animals do it has a structure which is inherently irrational: the weighting we give to a future event is, roughly, inversely proportional to how far away it is. This is hyperbolic discounting, and it is an empirically very well confirmed result.
I say "inherently irrational" because it is inconsistent over time: the relative cost of a day's wait is considered differently whether that day's wait is near or far. Looking at a day a month from now, I'd sooner feel awake and alive in the morning than stay up all night reading comments on lesswrong.com. But when that evening comes, it's likely my preferences will reverse; the distance to the morning will be relatively greater, and so my happiness then will be discounted more strongly compared to my present enjoyment, and another groggy morning will await me. To my horror, my future self has different interests to my present self, as surely as if I knew the day a murder pill would be forced upon me.
If I knew that a murder pill really would be forced upon me on a certain date, after which I would want nothing more than to kill as many people as possible as gruesomly as possible, I could not sit idly by waiting for that day to come; I would want to do something now to prevent future carnage, because it is not what the me of today desires. I might attempt to frame myself for a crime, hoping that in prison my ability to go on a killing spree would be contained. And this is exactly the behavour we see in people fighting akrasia: consider the alcoholic who moves to a town in which alcohol is not sold, anticipating a change in desires and deliberately constraining their own future self. Ainslie describes this as "a relationship of limited warfare among successive selves".
And it is this warfare which Ainslie analyses with the tools of behavioural economics. His analysis accounts for the importance of making resolutions in defeating akrasia, and the reasons why a resolution is easier to keep when it represents a "bright clear line" that we cannot fool ourselves into thinking we haven't crossed when we have. It also discusses the dangers of willpower, and the ways in which our intertemporal bargaining can leave us acting against both our short-term and our long-term interests.
I can't really do more than scratch the surface on how this analysis works in this short article; you can read more about the analysis and the book on Ainslie's website, picoeconomics.org. I have the impression that defeating akrasia is the number one priority for many lesswrong.com readers, and this work is the first I've read that really sets out a mechanism that underlies the strange battles that go on between our shorter and longer term interests.