Opportunity Cost (機會成本) 參考 Opportunity cost is the forgone benefit that would have been derived from an option not chosen. To properly evaluate opportunity costs, the costs and benefits of every option available must be considered and weighed against the others.

例如某甲現在有1小時時間，可挑選A、B、C三件同樣都需花費1小時才能完成的三件事之一來做，如果某甲選擇了A，便會放棄B和C，而因為某甲選擇了第一選擇，所以某甲的機會成本就是第二選擇（被放棄而價值最高，在這個例子是B）。這裡有一個特別需要注意的一個點，如果選擇了第二選擇，基於機會成本為價值最大者，因此某甲的機會成本是第一選擇（被放棄價值最大者）

Alternative Cost (替代性成本) 參考 Opportunity cost means a benefit that was passed up to pursue another venture.

機會成本，被放棄而價值最高的選擇（Highest-valued Option Forgone），又稱為替代性成本（Alternative Cost，就是俗語的世界上沒有白吃的午餐、魚與熊掌不可兼得。簡單來說，機會成本就是所犧牲的代價

 Invisible Hand  Adam Smith  (看不見的手 亞當 斯密) 參考 The invisible hand is a metaphor for the unseen forces that move the free market economy. Through individual self-interest and freedom of production and consumption, the best interest of society, as a whole, are fulfilled. The constant interplay of individual pressures on market supply and demand causes the natural movement of prices and the flow of trade.

看不見的手,一詞是18世紀英國經濟家斯密,1776年在《國富論中的命題。最初的意思是,個人在經濟生活中只考慮自己利益,受“看不見的手“驅使,即通過分工和市場的作用,可以達到國家富裕目的。後來, “看不見的手”便成為表示資本主義完全競爭模式的形象用語。這種模式的主要特征是有制人人為自己都有獲得市場信息的自由,自由競爭,無需政府干預經濟活動

Thinking at the margin (邊際思考) 參考 參考2 means to let the past go and to think forward to the next hour, day, year, or dollar that you expend in time or money. What’s better for you now or in the next few minutes? If you think at the margin, you are thinking ahead.