某种东西的成本是为了得到它而放弃的东西

The cost of something is what you give up to get it

Because people face trade-offs，making decisions requires comparing the costs and benefits of alternative courses of action.In many cases，however，the cost of some action is not as obvious as it might first appear．

Consider，for example，the decision whether to go to college.The benefit is intellectual enrichment and a lifetime of better job opportunities.But what is the cost?

To answer this question，you might be tempted to add up the money you spend on tuition，books，room，and board.Yet this total does not truly represent what you give up to spend a year in college．

The first problem with this answer is that it includes some things that are not really costs of going to college.Even if you quit school，you would need a place to sleep and food to eat.Room and board are costs of going to college only to the extent that they are more expensive at college than elsewhere.Indeed，the cost of room and board at your school might be less than the rent food expense that you would pay living on your own.In this case，the savings on room and board are a benefit of going to college．

The second problem with this calculation of is that it ignores the largest cost of going to college—your time.When you spend a year listening to lectures，reading textbooks，and writing papers，you cannot spend that time working at a job.For most students，the wages given up to attend school are the largest single cost of their education．

The opportunity cost of an item is what you give up to get that item.When making any decision，such as whether to attend college，decision makers should be aware of the opportunity costs that accompany each possible action.In fact，they usually are.College-age athletes who can earn millions if they drop out of school and play professional sports are well aware that their opportunity cost of college is very high.It is not surprising that they often decide that the benefit is not worth the cost．

某种东西的成本是为了得到它而放弃的东西

由于人们面临着权衡关系，所以，作出决策就要比较可供选择的行为方案的成本与收益。但是，在许多情况下，某种行动的成本并不像乍看时那么明显。

例如，考虑是否上大学的决策。其收益是使知识丰富并能拥有更好的工作机会。但成本是什么呢? 要回答这个问题，你会想到把你的学费、书籍、住房和伙食的钱加起来。但这种总和并不真正地代表你上一年大学所放弃的东西。

这个答案的第一个问题是，它包括的某些东西并不是上大学的真正成本。

即使你不上大学，你也需要有睡觉的地方，要吃东西。只有在大学的住宿和伙食比其他地方贵时，贵的这一部分才是上大学的成本。实际上，上大学的住宿和伙食费可能还低于你自己生活时所支付的房租与食物费用。在这种情况下，住宿与伙食费的节省是上大学的收益。

这种成本计算的第二个问题是，它忽略了上大学最大的成本——你的时间。当你把一年的时间用于听课、读书和写文章时，你就不能把这段时间用于工作。对大多数学生而言，为上学而放弃的工资就是他们受教育的最大单项成本。

一种东西的机会成本是为了得到这种东西所放弃的东西。当作出任何一项决策，例如，是否上大学时，决策者应该认识到伴随每一种可能的行动而来的机会成本。实际上，决策者通常是知道这一点的。那些到了上大学年龄的运动员如果退学而从事职业运动就能赚几百万美元，他们深深认识到，他们上大学的机会成本极高。因此，他们往往如此决定:不值得花费这种成本来获得上大学的收益。这一点儿也不奇怪。