A problem I see is that you can never be sure that it also works for other people. Just because one person reacts to a specific treatment does not mean that peo

A problem I see is that you can never be sure that it also works for other people. Just because one person reacts to a specific treatment does not mean that people on average react to the treatment in the same way. That’s the problem of having a sample size of 1. In other words: We cannot say much about whether the effect generalizes to a larger population from knowing that it has an affect on just one person.