Most people don't think they "could" cure Alzheimers by snapping their fingers, and so they don't feel terrible about failing to do this.
By contrast, people who fail to resist overeating, or who fail to stop playing Civilization at a reasonable hour, feel strongly that they "could have" resisted, and take this as a license to feel terrible about their decisions.
As I said last week, most people have broken "coulds."
Willpower is scarce in this world. Sometimes, you can will yourself out of a mental rut you're in, but only rarely; more often, sheer force of will alone is not sufficient. If your plan to stop staying up too late playing Civilization is "well I'll just force myself harder next time," then this plan is doomed to failure. If it didn't work last time, it likely won't work next time. Willpower is a stopgap, not a remedy.
I think that most people's "coulds" are broken because they put the action nodes in the wrong place. They think that the "choice" occurred at turn 347 of Civilization, when they decided to continue playing one more round (and at each following turn between midnight and 4:00 in the morning).
But that's not where the choice occurred. If you have to force yourself to change your behavior, then you've already missed the real choice node.
The actual choice occurs when you decide whether to play Civilization or not, at the very beginning.
Say you have one acquaintance in your social circles who regularly frustrates you, and every so often, you explode at them and get into a big shouting match. You know you shouldn't start yelling at them, you try to not be frustrated. Whenever they start annoying you, you will yourself to cool down, but it never quite works (no matter how strongly you resolve to force yourself harder next time). In this case, I suggest that you stop trying to force yourself to hold back as your frustration peaks, and instead start noticing what happens five minutes before you explode. That's where the real choice is. The real choice isn't in whether or not you explode in the moment, it's in whether you exit the situation five minutes earlier.
The real choices tend to happen a few minutes before the choices that people beat themselves up about. If you have to apply willpower, you've already missed the choice node. (In fact, I've previously suggested promising yourself that you'll never pull yourself out of a situation using willpower — knowing that you won't save your own ass if you get into a situation where you need willpower to extract yourself really makes you notice the true point of no return when it comes along.)
If you find yourself in a pattern of behavior you don't like, then I recommend pretending you don't have any willpower. Imagine you lived in the world where you couldn't force yourself to stop doing something addicting after starting. In that world, how would you act?
Look for the triggers that precede the action you wish you could make differently. What happens an hour beforehand? What happens five minutes beforehand? What happens sixty seconds before you fail to act as you wish?
That's where the real choice lies.
Most people's coulds are broken. They treat themselves like they "could" start bingeing a TV show and then stop at a reasonable hour. They put themselves in a situation that tempts them against their better judgement, and then berate themselves when they succumb.
By contrast, I don't treat myself as if I "could" stop binge-reading a good book, and therefore I don't feel terrible if I binge. Instead, I say, "ah, I see, I binge-read engaging books; I will treat 'read an engaging book' as a single atomic action that takes five to twenty hours, with no choice nodes in between." Where others are berating themselves for failing to complete an impossible task ("stop binge-reading halfway through and get back to real work"), I am learning what I am and am not capable of, and learning where my real action nodes are.
We humans don't have all the choice nodes. Sometimes, we can't stop binge-reading a good book anymore than we could snap our fingers to cure Alzheimer's disease. Sometimes, addiction takes over; other times, the lizard brain takes over; other times, primal rage takes over. In those moments, we don't get to call the shots. We aren't the choice-makers at every point in our lives. We often lack the willpower to override our impulses, instincts, and habits.
The goal is to win anyway.
Our better judgement is not the absolute arbiter of our actions, and there are often times when the voice of judgement is nearly powerless to affect our behavior. We aren't yet gods. We're still monkeys. Still neural nets.
I suggest you stop berating yourself for failing to complete impossible tasks, and start experimenting and identifying which action nodes work.
Search for the choices that let you act as you wish before the decision gets difficult to execute. Learn how to identify the moments when your mind is readily responding to your will. Those are the real choice-points, and it is from there that you may optimize.