Somehow, we feel as if merely feeling guilty is the appropriate and sufficient response to our self-punishment!
I think that's a special case of feeling as if feeling guilty is the appropriate and sufficient response to that kind of punishment (displays of disapproval or outrage, etc.) from anyone, and that comes about because feeling guilty often is taken as the appropriate and sufficient response to that kind of punishment.
Compare to, say, a politician who's been caught selling influence or having an affair, or a religious leader who's been caught using crystal meth and gay prostitutes, etc. They always seem so sincere in their public apologies and statements of regret and remorse... yet, suspiciously, all that tearful regret and all those acknowledgements of moral failing weren't enough to get them to actually stop doing the corrupt or hypocritical things in question until they got caught and publicly shamed, and even in their admissions of guilt they will still try to avoid giving up anything of substance (political office, religious leadership, etc.) if they can. I think that's pretty much what the emotion of guilt is — it's not a feeling of regret at actually having done something wrong, it's a response to the feeling of being judged negatively by someone whose opinion matters to you (whether for instrumental or terminal reasons). That's probably why self-inflicted guilt isn't useful for self-improvement: it's an emotion that's primarily about convincing people that you regret something and won't do it again, whether or not you really do regret it and plan to stop. More signaling than substance. In the social realm, this often balances out, because the things that provoke it — public displays of outrage, etc. — are often largely signaling as well, as there are plenty of reasons to appear outraged other than actually being outraged. It's a dynamic that's good for exerting power over people who care what you (appear to) think of them, but, for obvious reasons, not so good for self-control. Yet it's not surprising that we try to guilt-punish ourselves; we all have self-images we're trying to live up to, so in that sense we care about being judged negatively by ourselves, and if your 'thinker' and 'doer' have sufficiently out-of-sync preferences, such that they feel like different people to each other, then it is no surprise that they'll often invoke adaptations and habits that formed around interpersonal dynamics. So if I'm persistently doing something that I don't want myself to do, then the part of me that wants me to live up to some higher ideals will automatically execute the "display [and maybe feel] outrage" macro, and the part of me that wants to do something else will respond by executing by the "display and feel guilt" macro... the latter macro consisting not of necessarily changing the actual behaviour, but only changing it to the extent necessary to appear remorseful to a punisher assumed to be someone other than oneself.
(— or at least that's my guess as to what's going on, and I will now go off and worry about whether it's a just-so story and whether it's useful and whether it's testable.)
Edit: This reminds me of something parents often do. Punishment of children by parents often amounts to extracting apologies and displays of remorse from the child, with no particular expectation that the child should genuinely understand and regret what they did, or at least regret it for any reason other than the punishment itself. (Being asked/forced to apologize was always what confused me the most — usually parents say "Say you're sorry!" right away without actually convincing the child they did something wrong, so being told to apologize felt to me like being asked to lie.) Anyway, since people get used to being able to get away with things as long as they make a convincing show of looking sorry after getting caught (which, after enough time being a child, probably feels almost indistinguishable from actually feeling sorry), it makes sense that they'd generalize that rule and get into the habit of responding to their own self-punishment the same way, once they're broken enough that they start inflicting that kind of self-punishment at all.
The amusing part is that then people worry that displays of remorse extracted under punishment might not be sincere.
When you procrastinate, you're probably not procrastinating because of the pain of working.
How do I know this? Because on a moment-to-moment basis, being in the middle of doing the work is usually less painful than being in the middle of procrastinating.
(Bolded because it's true, important, and nearly impossible to get your brain to remember - even though a few moments of reflection should convince you that it's true.)
So what is our brain flinching away from, if not the pain of doing the work?
I think it's flinching away from the pain of the decision to do the work - the momentary, immediate pain of (1) disengaging yourself from the (probably very small) flow of reinforcement that you're getting from reading a random unimportant Internet article, and (2) paying the energy cost for a prefrontal override to exert control of your own behavior and begin working.
Thanks to hyperbolic discounting (i.e., weighting values in inverse proportion to their temporal distance) the instant pain of disengaging from an Internet article and paying a prefrontal override cost, can outweigh the slightly more distant (minutes in the future, rather than seconds) pain of continuing to procrastinate, which is, once again, usually more painful than being in the middle of doing the work.
I think that hyperbolic discounting is far more ubiquitous as a failure mode than I once realized, because it's not just for commensurate-seeming tradeoffs like smoking a cigarette in a minute versus dying of lung cancer later.
When it comes to procrastinating, the obvious, salient, commensurate-seeming tradeoff, is between the (assumed) pleasure of reading a random Internet article now, versus the (assumed) pain of doing the work now. But this, as I said above, is not where I think the real tradeoff is; events that are five minutes away are too distant to dominate the thought process of a hyperbolic discounter like a human. Instead our thought processes are dominated by the prospective immediate pain of a thought, a cost that isn't even salient as something to be traded off. "Working" is an obvious, salient event, and "reading random articles" seems like an event. But "paying a small twinge of pain to make the decision to stop procrastinating now, exerting a bit of frontal override, and not getting to read the next paragraph of this random article" is so map-level that we don't even focus on it as a manipulable territory, a cost to be traded off; it is a transparent thought.
The real damage done by hyperbolic discounting is for thoughts that are only very slightly painful, and yet, these slight pains being immediate, they manage to dominate everything else in our calculation. And being transparent, we aren't even aware that's what's happening. "Beware of immediately trivially painful transparent thoughts", one might say.
Similarly, you may read a mediocre book for an hour, instead of a good book, because if you first spent a few minutes to search your library to obtain a better book, that would be an immediate cost - not that searching your library is all that unpleasant, but you'd have to pay an immediate activation cost to do that instead of taking the path of least resistance and grabbing the first thing in front of you. It's a hyperbolically discounted tradeoff that you make without realizing it, because the cost you're refusing to pay isn't commensurate enough with the payoff you're forgoing to be salient as an explicit tradeoff.
A related note that I might as well dump into this post: I'm starting to think that procrastination by reading random articles does not cause you to rest, that is, you do not regain mental energy from it. Success and happiness cause you to regain willpower; what you need to heal your mind from any damage sustained by working is not inactivity, but reliably solvable problems which reliably deliver experienced jolts of positive reinforcement. Putting in the effort to read a good book may do this; playing a good computer game may do this; reading random Internet articles, or playing bad games, probably won't. Literal mental exhaustion might mean that you don't have enough energy left to read a good book - or that you don't have enough energy left to pay the immediate cost of searching your library for good reading material instead of mediocre reading material - but in this case you shouldn't be reading random online articles. You should be sitting with your eyes closed listening to music, or possibly even napping; if dealing with a truly exhausted brain, reading random articles is probably too much effort.
If you don't feel good while reading a lot of forgettable online articles, and you don't feel renewed after doing so, your intuitive theory which says that this is how to rest is mistaken, and you need to look for other ways to rest instead - more active ways to regain willpower, less active ways to recover from immediate exhaustion. In general, poor performance often indicates poor models; if something seems incredibly difficult to predict or manipulate, it may be that you have mistaken beliefs about it, including transparent mistakes that are nonquestioned because they are nonsalient. This includes poor performance on the problem of resting.
Hopefully publishing this post will help me live up to it.