In the world of cost accounting, there's a concept known as contribution margin. Basically, it's how much you make on a product or service after you consider how much it cost to make that thing. The formula is revenue less the variable costs that go into making the product. Contribution margin is an important metric for businesses because it tells you whether you are making a profit on the things you sell. After all, it would do no good to sell a bunch of t-shirts for $18 a piece, if each of them costs you $20 to make!

Now, Jesse asks, what if we apply this concept to our life? We have jobs that earn us revenue. What do they cost to do? Time, obviously, but perhaps also driving/commuting, stress? The point is, the things that earn us money have a non-zero cost associated with them, and it's wise to keep track of that cost and make sure, at the end of the day, that we are using our time in a profitable manner.

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