Suppose you're trying to add up 4,000 numbers. You need to get the answer as soon as possible, so you think about how best to do the task. You might say, "Well, getting the job done quickly is important, so let me squint my eyes, roll up my sleeves, and concentrate really hard, so that I can have as much mental focus as possible while I get through this." You then proceed to use a pencil and paper to add the digits, sweating and wrinkling your brow as you focus your concentration for the next 10 hours until the task is complete. Meanwhile, your friend downloads the digits to a computer, pastes them into Excel, and figures out the answer a minute later.
Ah, the power of macro-optimization! I've noticed a number of instances in which I and other people tend to get overly caught up in thinking about micro-level decisions on a day-to-day basis, without spending enough time improving higher-level structural choices. For instance, Should I procrastinate for another X minutes? Should I keep exercising or stop? Do I go for one more helping of dinner? Shall I spend money on purchasing this small item that I could live without?
These are all important questions, and their answers are not irrelevant. It is important to avoid procrastinating, not to waste money on luxuries, and so forth. There is a place for exerting effort in these decisions. But if you find yourself burning up willpower on such questions on a regular basis, then you're probably doing something wrong. In general, life doesn't have to be a day-in-day-out struggle to "do the right thing" by sheer force of effort. Very often, there are big-picture changes and/or rules that you can put in place such that the micro-optimizations become minor or altogether unnecessary.
One case where this applies is with food choices. I've found that if I buy junk food and have it around the house, the day becomes a constant willpower struggle with the question, Shall I go ahead and eat another cookie or not? But if I don't buy the junk food in the first place, and if I go for a long enough period that my cravings for it subside, then the question vanishes from my mind, and I don't think about cookies at all. Similarly, many people find that going completely vegetarian is easier than going almost-vegetarian, just because the question, "Should I eat meat on this particular occasion?" doesn't constantly arise. (That said, others find that near vegetarianism is easier than complete vegetarianism. And of course, it's important to consider the widely variable impacts of different types of animal foods.)
In other cases, the best solution may be not to set a rule to do the right thing but, rather, to allow oneself to do the wrong thing with the bargain of doing the right thing in another area of higher value. For instance, I sometimes feel guilty about not doing some tangible action that would prevent a little bit of immediate suffering -- e.g., looking for injured worms stranded on the sidewalk that could be put out of their misery on a rainy day. Sometimes I do stop to help the worms, but at other times, I instead promise myself to put in extra effort later toward another action with greater value (like promoting awareness of the general problem of worm suffering in the wild). I also sometimes feel guilty about spending money to buy chewing gum, because it's a "junk food" that I could clearly live without; but I've noticed that there are a number of other areas of my grocery budget where I could more painlessly reduce costs, and I promise myself that I'll make bigger cuts there in return for keeping the gum. Similarly, rather than going vegetarian, some might find it easier to continue to eat meat personally and to instead donate, say, an extra $100 a year to The Humane League, with the latter action having a bigger total impact on animal suffering.
(One complication with "willpower bargains" of this sort is that you have to make sure you actually will do more of the activity that's more efficient than you were going to beforehand. If you feel like you're at the limits of your willpower and may burn out if you work any harder, then optimizing where you expend willpower is the best choice. On the other hand, if you think you can build your willpower muscle stronger by using it more than you already do, then consider doing that first.)
Similar thinking applies in many other areas. For instance, say you're persuaded by Singer's argument in "Famine, Affluence, and Morality" but don't want to live at the level of a Third World peasant. You could probably do better by continuing to live a normal lifestyle in a First World country, taking a high-paying job, and donating your earnings. Chances are that even a spendthrift investment banker will have more cash left over to donate (to, say, Vegan Outreach or The Humane League) than the most frugal of secretaries or farm workers. In addition, rather than hyper-optimizing your own income, it's worth considering whether you could achieve more total donations for a given cause by spending less time on work and more time networking with friends and colleagues who might contribute.
Finally, the same sorts of logic apply with respect to where one donates. To use a slogan of Givewell, "Don't give more; give well." If you can forgo a fifth of your potential donatable funds to spend time on research that will double the cost-effectiveness of your final donation, you will have made more total impact.
The questions about willpower and personal effort may seem different than those about allocation of time and money. On the inside, it often feels as though we should be able to make the right individual choices on every occasion. Sure, we can't blame people for having limited budgets or a finite number of hours in the day, but when they expend money on a product they could have lived without, or when they waste time on a fun activity instead of working more, it sometimes feels like they're blameworthy, because "they could" have done differently. But the fact of the matter is, willpower, energy, and motivation are themselves finite resources, and sometimes "wasting time" on having fun is the right choice. Rather than feeling guilty about every little apparently sub-optimal decision that you make, try to direct your guilt toward those areas that you rationally observe have the highest value.
In many ways, this relates back to the post on salience and motivation. The micro-optimization choices that we face are clear and immediate: It feels morally important to make the right decision in those cases, and we feel bad about ourselves when we don't. Yet -- as the case of adding 4,000 numbers illustrates -- many times there are solutions beyond sheer force of will that can end up making a bigger real-world impact. Moralizing isn't the answer to every problem. And indeed, because willpower is limited, expending guilt should only be a last resort: Sometimes there are other structural changes you can make (to your work environment, your purchasing habits, your topics of mental focus, your social activities, and so on) that will eliminate the willpower dilemmas altogether. In other words, focus on finding the right rules more than on forcing yourself to do the apparently optimal thing in each situation; the latter is a recipe for burnout.
(I suppose this discussion is relevant to the act- vs. rule-utilitarianism debate, among other things.)