Put simply, the miracle count is the number of unlikely events that we need to happen for a project to succeed.
If your startup needs zero miracles to work, it probably isn't a defensible startup. If your startup needs multiple miracles, it probably isn't going to work because of how these miracles stack. With every miracle, you are multiplying in another low probability event to get an even smaller expected outcome.
Therefore, Exactly One Miracle.
Inspired by https://glazkov.com/2021/08/20/the-miracle-count/
Relatedly, Choose boring technology