003 Sunk cost

What you have paid for it is named as "Sunk cost", a cost that has already been incurred and cannot be recovered.
Customers would like to pay for something more just because they had paid for it before.
So, you could take 2 principles in your business model:

1. Let the customers pay more and more, little by little.
2. Give the customers more "cheap goods" to lower their expectations.

沉没成本指所有你付出的，是一种已经发生且无法收回的成本。
消费者更倾向于因为他曾经为某样东西付出过，而付出。
所以，你可以在你的商业模型中使用这两个原则：

1. 让消费者一点一点地付出更多
2. 给消费者更多“廉价商品”来降低他们的预期。