Meet Bean Mail, a made-up coffee subscription: one box of fresh beans a month for $30. Every number in this lesson is Bean Mail's, and each step reuses the one before.

Revenue (sales) is all the money coming in. Profit is what's left after every cost.

Try it: drag the slider. How many customers until something is left over?

Bean Mail has three kinds of cost: the boxes themselves (more customers, more boxes), the team and rent (the same every month) and marketing. Busy isn't the same as profitable.