更加简单的讲，就是指你为了从实某件事情而放弃其他事情的价值。
我们常拿融资租赁和贷款比较谁的融资成本高？如果不把机会成本加进去的话，可能会得出一个不正确的结论。比如人们通常感觉融资租赁的融资成本比银行贷款高。出现这种认识错误的主要在于没有把机会成本考虑进去。
首先从利率上说租赁公司的资金是从银行来的，因此融资成本一定比银行高。但从机会成本考虑就不一定了。银行贷款是以资金占用作为标的的。融多少资金，就可以算出有多大的成本。融资租赁是以租赁物件的标的为基础计算成本的，有些厂商租赁打出“零”利率的口号，实际上是一种促销手段。天下没有免费的宴席，从物件的采购上早已把利息提前纳入销售价格中去了。
因为上述原因，和租赁公司谈利率，实际上没有什么太大的意义。融资租赁的会计处理上可能会遇到利率问题，但不是租赁公司给出的利率，而是租赁公司的收益率。是用来财务处理的，不能真正地反映融资成本。
第二个概念是银行的利率比租赁公司高。因为银行的利率不能随意加减，有政策限制。租赁公司的利率可以根据双方的讨价还价来确定，有政策支持。但是，银行的政策现在也开始变化，实际上贷款利率已经是上不封顶。对于信用稍差的企业，银行贷款的利率也不会低。融资租赁因为增加了一道物权保障，也是做银行的次好项目。从利率上看不会有太大的差别，因为银行要做这种项目也要很高的利率。
第三融资租赁项目的操作程序要比银行贷款公开的多，申办程序要简单一些，谈判各方的地位要平等一些。请客吃饭，回扣等桌下交易要少一些，成交时间要快一些。如果把提前投产带来的效益算进去，使用融资租赁的机会成本比银行贷款要小的多。
第四是融资租赁在税收上有独特的好处，是任何融资方式都得不到的。加上审批过程简单，这就是为什么在国外，融资租赁成为中小企业融资的主渠道的一个重要原因。
工程机械设备的客户70%以上是中小企业，他们没有雄厚的实力到银行去搞公关，银行对小金额的融资也不感兴趣。因此在银行偿受到按揭贷款的痛苦后停止了用这种方式给企业融资。融资租赁也就在这个时候悄然兴起。
在新经济的环境下，人们多少要有一些财务知识，这就是通常所说的“财商”（智商以外的另一种智慧），融资租赁的真正含义应该是财务租赁（在英文中，财务、金融、融资都是一个词）。这样即可以解决融资难的问题，有可以降低机会成本的花消。
机会成本在经济学上是一种非常特别的既虚既实的一种成本。它是指1笔投资在专注于某一方面后所失去的在另外其它方面的投资获利机会。
萨缪尔森在其《经济学》中曾用热狗公司的事例来说明机会成本的概念。热狗公司所有者每周投入60小时，但不领取工资。到年末结算时公司获得了22000美元的可观利润。但是如果这些所有者能够找到另外其它收入更高的工作，使他们所获年收达45000美元。那么这些人所从事的热狗工作就会产生一种机会成本，它表明因他们从事了热狗工作而不得不失去的其它获利更大的机会。对于此事，经济学家这样理解：如果用他们的实际盈利22000美元减去他们失去的45000美元的机会收益，那他们实际上是亏损的，亏损额是45000－22000＝23000美元。虽然实际上他们是盈利了。
那么如何理解上述这种现象呢？
我们设想他们（以自己的劳动）投入热狗工作P所得的收益仍然是22000美元，而（以相同的劳动）投入某种工作Q所得的收益也是45000美元。那么按照人们所理解的机会成本概念，他们投入工作P的机会成本是工作Q的收益即45000美元，同样，投入工作Q的机会成本是工作P的收益即22000美元。工作P、Q之收益互为对方的机会成本。
但是实际上，由于任何一个单位的投资（无论是劳动投资还是资金投资）都具有专注性，因此不能设想投资获得二注收入（所谓“二注”即是指同时分为2个或多个方面的注入，如1个单位投资额分为2个注入方面，这是不可能的。1个单位的投资额只能在同一时间专注于某个行业的某一点上，这即是“投资专注”性）。通俗地说，1笔投资不能同时被假设为获得2笔（或2笔以上）投资的收益。所以在计算机会成本时我们不能用1笔投资的二注收入来叠加，也不能用它的二注成本耗费来叠加。比如我们不能算他们在从事热狗工作的过程中又再想同时获得工作Q的收益，以致如果不能获得这个收益就认为产生了机会成本。如果他们真能获得这样的二注收益，那么他们应该获得22000＋45000美元的二注收入，而不单止22000或45000美元。
但以上人们通常所认为的“工作P、Q之收益互为对方的机会成本”似乎具有这种投资与收益的二注性，因为它想在获得当前的工作P之收益的同时，又想要获得工作Q的收益，当不能获得工作Q的收益时，就被认为是亏损的。特别是当已经获得较高收益的同时还想得到较低收益的情况。比如当从事工作Q已经获得比工作P更多的收益时，还想到失去了工作P的更少收益，这样的话，所理解的机会成本就不对了。
实际上机会成本应该是这样：工作P对于工作Q来说具有机会成本，但工作Q对于工作P来说就已经没有机会成本了，因为工作P的收益比工作Q小。因此所谓机会成本实际上只是“相对机会成本”而没有绝对机会成本。当一个人正在从事的工作收益比较低时，相对于你所能从事的更高收益的工作来说，就产生了机会成本。比如一个人能够做经理和教师，而经理工作的收入显然要比教师的收入大，因此当你从事教师工作时，相对于经理工作来说你就存在着一个机会成本的问题，但是我们不能反过来，说从事经理工作会使你失去教师工作的更低收入，从而产生一个机会成本。收入大的工作相对于收入小的工作来说，是没有机会成本的，因为你已经找到了一个更好的机会使你更好的收入。在此所谓“机会”实际上就是寻求更大利益的机会，既然获得了更大利益，那么因失去机会所导致的利益丧失也就相对没有了。
那么，由于从事工作P比从事工作Q所获得的收入较小而产生了机会成本，其机会成本量是工作Q的收入减去工作P的收入，即45000－22000＝23000美元。他们因此亏损了23000美元。如果他们的工作P的收入渐渐提高，从22000达到40000，则他们所失去的机会成本只是45000－40000＝5000美元。如果他们的工作P的收入再提高到与工作Q相等的45000，则他们的工作P与工作Q对比就只有等于零的机会成本了，即45000－45000＝0。如果工作P的收入再提高到比如50000，则他们从事工作P的机会成本相对于工作Q来说就是45000－50000＝－5000美元，机会成本为负数。机会成本为负数表明什么呢？表明他们工作P相对于工作Q来说已经非但没有机会成本，而是还大大“抵值”呢！由于成本作为一种代价耗费是总是趋向于最小化的，因此从事一项工作，它的机会成本越小越好，它的最小值自然要包括0值以下的负数。
Opportunity cost is the cost (sacrifice) incurred by choosing one option over an alternative one that may be equally desired. Thus, opportunity cost is the cost of pursuing one choice instead of another. Every action has an opportunity cost. For example, someone who invests $10,000 in a stock denies oneself the interest that one can earn by leaving the $10,000 dollars in a bank account instead. Opportunity cost is not restricted to monetary or financial costs: the real cost of output forgone, lost time, pleasure or any other benefit that provides utility should also be considered.
Opportunity cost is a key concept in economics because it implies the choice between desirable, yet mutually exclusive results. It has been described as expressing "the basic relationship between scarcity and choice."
Example:
Actual Resale Value (ARV) = Original price / 2 - £0.10
If a city decides to build a hospital on vacant land it owns, the opportunity cost is the value of the benefits forgone of some other thing which might have been done with the land and construction funds instead. In building the hospital, the city has forgone the opportunity to build a sports center on that land, or a parking lot, or the ability to sell the land to reduce the city's debt, since those uses tend to be mutually exclusive. Also included in the opportunity cost would be what investments or purchases the private sector would have voluntarily made if it were not taxed to build the hospital. The total opportunity costs of such an action can never be known with certainty (and are sometimes called "hidden costs" or "hidden losses", what has been prevented from being produced cannot be seen or known). Even the possibility of inaction is a lost opportunity (in this example, to preserve the scenery as-is for neighboring areas, perhaps including areas that it itself owns).
It can also apply to time; one might use a limited vacation time to travel to a place of cultural enrichment or to do household improvements. Thus the two-week road trip might preclude repairing or painting one's house that year. To the vast majority of people, time has value.
Evaluation
Opportunity cost needs not be assessed in monetary terms, but rather can be assessed in terms of anything which is of value to the person or persons doing the assessing (or those affected by the outcome). For example, a person who chooses to watch, or to record, a television program cannot watch (or record) any other at the same time. (The rule still applies if the recording device can simultaneously record multiple programs; there is going to be a limit, and if the number of desired programs exceeds the capacity of the recorder, some of them will not be saved, and thus cannot be seen.) In any case, at the time the person chooses to watch a program, either live or on a recording, they cannot watch something else, and if they are not able to record another program showing at the same time, the opportunity to view it is lost (presuming the particular program is not repeated). Or as another example, someone having a video game can choose to watch a program or play the video game on the TV; they can't do both simultaneously. Whichever one they choose is a lost opportunity to experience the other. Or for that matter, a lost opportunity to engage in some other activity entirely (exercising outdoors, or visiting with family or friends, as merely two examples).
The consideration of opportunity costs is one of the key differences between the concepts of economic cost and accounting cost. Assessing opportunity costs is fundamental to assessing the true cost of any course of action. In the case where there is no explicit accounting or monetary cost (price) attached to a course of action, ignoring opportunity costs may produce the illusion that its benefits cost nothing at all. The unseen opportunity costs then become the implicit hidden costs of that course of action.
Note that opportunity cost is not the sum of the available alternatives, but rather of benefit of the best alternative of them. The opportunity cost of the city's decision to build the hospital on its vacant land is the loss of the land for a sporting center, or the inability to use the land for a parking lot, or the money which could have been made from selling the land, or the loss of any of the various other possible uses—but not all of these in aggregate, because the land cannot be used for more than one of these purposes.
However, most opportunities are difficult to compare. Opportunity cost has been seen as the foundation of the marginal theory of value as well as the theory of time and money.
In some cases it may be possible to have more of everything by making different choices; for instance, when an economy is within its production possibility frontier. In microeconomic models this is unusual, because individuals are assumed to maximise utility, but it is a feature of Keynesian macroeconomics. In these circumstances opportunity cost is a less useful concept.