User costs

When thinking about retention, it's useful to think about:

1. Switching costs: how expensive it is for users to drop the system
2. Multihoming costs: how expensive it is for users to use multiple systems at the same time

[#julian-defaults]: Lehr, Julian. “Julian.Digital - The Power of Defaults.” Julian.Digital (blog), December 20, 2021. https://julian.digital/2021/12/20/the-power-of-defaults/.