Why can't we stop? We can blame evolution, which has produced in us instincts that compel us to gorge ourselves when food is abundant, to build up fat reserves for the lean months. These instincts are not helpful to us when there is an all-you-can-eat buffet nearby that's open year-round. These instincts are not even specifically ours: other animals don't know when to stop either. Butterflies will feast on fermented fruit until they are too drunk to fly. Pigs will eat acorns until they are too fat to stand up and have to resort to crawling about on their bellies in order to, yes of course, eat more acorns. Americans who are too fat to walk are considered disabled and the government issues them with little motorized scooters so that they don't have to suffer the indignity of crawling to the all-you-can-eat buffet on their bellies. This is considered progress.
Or we can blame our education, which puts mathematical reasoning ahead of our common sense. Mathematics uses induction—the idea that if 1 + 1 is 2 then 2 + 1 must be 3, and so on up to an arbitrarily large quantity. In the real world, if you are counting acorns, then 1 + 1 acorns is not the same as 1,000,000 + 1 acorns—not if there are squirrels running around, which there will be once they find out that you are the one who's been stealing their acorns. A million acorns is just too many for you to keep track of, and your concerted effort to keep adding one more to the pile while fighting off squirrels may cause small children to start calling you silly names. The bigger the pile grows, the more likely you are to have to take inventory, and in the process you are increasingly likely to make a mistake, so that it turns out that 1,000,000 + 1 is in fact 1,000,001 - δ, where δ is the number of acorns you have lost track of, somehow. Once δ > 0, you have achieved diminishing returns, and once δ > 1, you have achieved negative returns. In the real world, the bigger you think a number should be, the smaller it actually turns out to be. At some point, trying to add one more to the pile becomes a particularly wasteful way of making the pile smaller. This result is not intellectually pleasing, and there is no theory to back it up, but it is observable anywhere you care to look. The fact that we are unable to adequately explain any given phenomenon by using our feeble primate brains does not make it any less real.
The concept of diminishing returns is quite simple for most people to understand and to observe, but notoriously difficult to detect for the person who is at the point of achieving them. The point of negative returns is even harder to detect, because by that point we tend to be too far gone to detect much of anything. If you already had N drinks, can you tell if you are at the point of diminishing returns yet? Will another drink make you happier and more sociable, or will it not make much of a difference? Or will it cause you to embarrass yourself and spend the next day nursing a debilitating hangover? Or will it send you to the emergency room to be treated for vomit inhalation? As a general rule, the more you imbibe, the more difficult it becomes for you to draw such fine distinctions. This rule does not seem to be limited to drinking, but applies to almost all behaviors that produce a feeling of euphoria rather than the simple satisfaction of needs. Most of us can stop ourselves from drinking too much water, or eating too much porridge, or stacking too many bales of hay. Where we do tend to run into trouble with self-control is when it comes to things that are particularly pleasurable or addictive, such as drugs, tobacco, alcohol, and rich and delicious food. And we tend to lose it completely when it comes to euphoria-inducing social semi-intangibles: satisfaction of greed, status-seeking, and power over others.
Is this the best we can do? Certainly not! Human culture is full of examples where people stood up and successfully opposed such primitive tendencies within themselves. The ancient Greeks made a virtue of moderation: the temple of Apollo at Delphi bore the inscription MHΔEN AΓAN—"Nothing in excess." Taoist philosophy focuses on the idea of balance between yin and yang (阴 阳)—seemingly contrary natural forces that in fact work together and must be kept in balance. Even in contemporary engineering culture one sometimes hears the motto "Better is the enemy of good enough." Sadly, though, engineers who are good enough to abide by it are something of a rarity. At the micro level of solving specific problems most engineers do strive to achieve the clever optimum rather then the stupid maximum, but at the macro level the surrounding business culture forces them to always go for the stupid maximum (maximum growth, revenue and profits) or the stupid minimum (minimum cost, product cycle time and maintainability). They are forced to do so by the influence of a truly pernicious concept that has insinuated itself into most aspects of our culture: the concept of competition.
The concept of competition seems to have first been elevated to cult status by games that were played as a form of sacrifice before gods, in cultures as different as ancient Greece and the Mayan civilization, where competitive events were held to please their various deities. I much prefer the Olympic version, where the object of the games was to express the ideal of human perfection in both form and function, rather than the Mayan version, where the outcome of the game was used to decide who would be sacrificed on the altar of some peculiar cultural archetype, but being open-minded I am ready to accept either as valid, because both are competitions in defense of principle. It was Aristotle who pointed out that pursuit of principle is the one area where moderation is not helpful, and who am I to refute Aristotle? But when moving from defending an ideal or a principle to performing mundane, practical, utilitarian functions it is the idea of competition itself that should be offered up as a nice, sizzling-fat burnt offering on the altar of our common sense.
If the goal is to achieve an adequate result with a minimum of effort, then why would two people want to compete to do the job of one? And if there is in fact work enough for two, then why wouldn't they want to cooperate instead of wasting their precious energies in competition? Well, they may have been brainwashed into thinking that they must compete in order to succeed, but that's beside the point. The point is that there is a major difference between competing for the sake of a principle—such as the perfection of divine creation—and competing for mere money. There is nothing divine about a big pile of money, and, just as with a big pile of acorns, the bigger the pile, the more "squirrels" it tends to attract. In fact, those who are sitting on some of the bigger piles of acorns often seem rather squirrely themselves. To mix metaphors, they also tend to be chicken-like, roosting on their acorns and expecting them to hatch into more acorns. But be they squirrels or be they chickens, or be they drug-addled mutant chicken-squirrels on steroids, they are certainly not gods, and their acorns are not worthy of our sacrifice.
Once we dispense with the idea that competition is in any sense necessary, or even desirable, new avenues of thought open up. How much is enough? Probably much less than we have now. How hard do we need to work for it? Probably a lot less hard than we are working now. What happens if we don't have enough? Well, perhaps then it's time to try working just a tiny bit harder, or, better yet, perhaps it is time to take a few acorns from those who still have too many. Since having too much is such hard work (mind the damn squirrels!) we'd only be helping them. We certainly don't want to keep up with them, because we know where they are headed—a quaint, exclusive little place called collapse. What we should probably be trying to do instead is to establish some sort of balance, where enough is, in fact, enough.