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♪ [音乐] ♪

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在经济学中

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你会经常听到 “边际” 这个词

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边际效益

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边际成本

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边际收益

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这样的例子不胜枚举

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那么经济学家认为边际是什么呢？

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为什么很重要呢？

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边际只是多一点或少一点的意思

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[]

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我们想象一下你正在看一部电影

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而你听不到对白

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你将音量稍微调高一点

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[来自电影的声音]

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你应该调高几多？

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嗯，这是比较增加音量的

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边际效益和边际成本的问题

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增加一格音量听起来不错

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现在你可以听到演员的对白

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[声音稍微大一点]

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你再增加了一格音量

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[声音更大]

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扬声器有点失真
但你还是比较喜欢这样子

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[声音更大]

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再增加一格

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[声音爆炸]

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嗯—哦

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现在是动作场面

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太大声了

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你不想吵醒室友

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于是你降低一格

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[声音更小]

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继续这样做

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边际地调高调低

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将每一步的边际效益与边际成本进行比较

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[]

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边际的考虑意味着

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将下一个决策的效益与其成本进行比较

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要注意，边际的考虑—

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是达成最理想或最佳决策的一种方法或途径

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[]

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如果我问你看电影用什么音量最好

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你可能难以回答

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但如果你一直在边际上思考和行动

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你会到达边际收益等于边际成本—

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[]

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这是最理想的情况

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因此，边际思考

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是寻找和找到答案的一种方式

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否则可能会很难才找到问题的答案

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边际思考

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还告诉你一些其他重要的事情

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不该考虑的事情

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假设你经营一家小型服装店

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而你认为 20 世纪 70 年代即将迎来复兴

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我记得那些时候

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♪ [音乐] ♪

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因此你买了 100 条牛仔喇叭裤

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假设支付了 75 美元一条

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你把牛仔裤定价为 100 美元—

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这能够支付你的成本，包括租金和工资

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但不幸的是，牛仔裤卖不出去

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- 什么？
- 你要做什么呢？

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你会考虑降价

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但你的会计师告诉你

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如果把售价降到 100 美元以下

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你肯定会蒙受损失

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[尖叫音效]

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幸运的是，你在高中或大学

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上过很好的经济学课

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所以你记得

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你为牛仔裤付的钱是无关紧要的

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这是沉没成本

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现在重要的是

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比较你的选项的边际效益和边际成本

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[]

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One option would be to put
the jeans in storage and hope,

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hope they'll come back in style.

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Maybe you can get $100
per pair in the future,

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but you get no money now,

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plus you have to pay for storage.

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Another option is to slash prices.

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Sell them all now for $50 each.

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That lets you clear out
your inventory

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and invest in something else.

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You choose option two

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and invest in the next big thing:

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leg warmers!

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Now, I know this sounds simple,

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but actually, even experienced
businesspeople --

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they often focus too much
on what they paid for an item

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and not enough
on their best choices right now.

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It's called the sunk cost,
or fixed cost fallacy.

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In fact, I snuck an example
of the fallacy right past you.

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Did you catch it?

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Earlier, I said you price
the jeans at $100 --

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a price that will cover your costs,
including rent and wages.

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But that's also wrong.

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If bell-bottom jeans turn out to be
in huge demand, for example --

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then you should price them
for more than $100.

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What you paid for the jeans
is irrelevant --

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whether your decision
was a bad one or a good one.

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People fall prey
to this kind of error all the time,

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especially holding on
to past mistakes.

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Maybe you've been told,
"Never give up!"

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Well, take the advice
of an economist.

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Sometimes giving up
is the smart thing to do.

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Is the movie
you're watching boring?

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Well, buying the ticket
was a bad decision.

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But that cost is sunk.

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Don't throw good time after bad.

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Walk out!

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No one likes to admit
that they made a bad decision,

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and so they stay
in bad relationships,

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bad businesses, and bad careers,

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hoping, hoping
to turn things around

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and prove that their past decisions
weren't so bad after all.

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An economist says,
"Ignore what you can't change.

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Ignore the past.
Focus on the future."

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Let's summarize
thinking on the margin.

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First, think about
a little bit more

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or a little bit less,

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and keep going
until you'll arrive at a point

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where the marginal benefits
equal the marginal costs.

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That's the optimum.

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Second, when making a choice,

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only think about
the costs and benefits

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that change with that choice.

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Ignore sunk costs.

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Thinking on the margin --

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it's useful,

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and not just for Economics classes.

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But if you are teaching
an Economics class,

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check out our free unit plan
that incorporates this video.

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I promise, the marginal benefit
will exceed the marginal cost.

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And if you're ready
to test yourself,

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check out our practice questions.

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Finally, if you're ready
for more microeconomics,

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click for the next video.

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♪ [music] ♪