Samuel Johnson called it the vanity of human wishes, and Buddhists talk about the endless cycle of desire. Social psychologists say we get trapped on a hedonic treadmill. What they all mean is that we wish, plan and work for things that we think will make us happy, but when we finally get them, we aren't nearly as happy as we thought we'd be.
vanity：虚荣心，空虚，浮华 get trapped：被困，陷于 hedonic：快乐论，享乐的 treadmill：跑步机，蹋车，单调的工作
Summer makes this particularly vivid. All through the busy winter I longed and planned and saved for my current vacation. I daydreamed about peaceful summer days in this beautiful village by the Thames with nothing to do but write. Sure enough, the first walk down the towpath was sheer ecstasy -- but by the fifth, it was just another walk. The long English evenings hang heavy, and the damned book I'm writing comes along no more easily than it did in December.
vivid：生动的，鲜明的 daydream about：幻想，梦想 towpath：牵道 ecstasy：狂喜，入迷，忘形 hang heavy：过的漫长而无聊
This looks like yet another example of human irrationality. But the economist Arthur Robson has an interesting evolutionary explanation. Evolution faces what economists call a principal-agent problem. Evolution is the principal, trying to get organisms (its agents) to increase their fitness. But how can it get those dumb animals to act in accordance with this plan? (This anthropomorphic language is just a metaphor, of course -- a way of saying that the fitter organisms are more likely to survive and reproduce. Evolution doesn't have intentions.)
irrationality：不合理，无理性 anthropomorphic：类人的，拟人 metaphor：隐喻，暗喻
For simple organisms like slugs, evolution can build in exactly the right motivations (move toward food and away from light). But it is harder with a complicated, cognitive organism like us. We act by imagining many alternative futures and deciding among them. Our motivational system has to be designed so that we do this in a way that tends to improve our fitness.
Suppose I am facing a decision between two alternative futures. I can stay where I am or go on to the next valley where the river is a bit purer, the meadows a bit greener and the food a bit better. My motivational system ensures that when I imagine the objectively better future it looks really great, far better than all the other options -- I'll be so happy! So I pack up and move. From evolution's perspective that is all to the good: My fitness has increased.
meadow：草地
But now suppose that I have actually already made the decision. I am in the next valley. It does me no additional good to continue admiring the river, savoring the green of the meadow and the taste of the fruit. I acted, I have gotten the benefit, and feeling happy now is, from evolution's perspective, just a superfluous luxury.
savor：尽情享受，品味 superfluous：多余的，奢侈的
Wanting to be happy and imagining the happy future made me act in a way that really did make me better off; feeling happy now doesn't help. To keep increasing my fitness, I should now imagine the next potential source of happiness that will help me to make the next decision. (Doesn't that tree just over the next hill have even better fruit?)
It is as if every time we make a decision that actually makes us better off, evolution resets our happiness meter to zero. That prods us to decide to take the next action, which will make us even better off -- but no happier.
Of course, I care about what I want, not what evolution wants. But what do I want? Should I try to be better off objectively even if I don't feel any happier? After all, the Thames really is beautiful, the meadows are green, the food -- well, it's better in England than it used to be. And the book really is getting done.
Or would it be better to defy evolution, step off the treadmill of desire and ambition and just rest serenely at home in Buddhist contentment? At least we humans can derive a bit of happiness, however fleeting, from asking these questions, perhaps because the answers always seem to be just over the next hill.
prod：戳，刺 serenely：安祥地，宁静地 fleeting：短暂的，稍纵即逝的