Observability, for one. In the article, the author talks about the Y-junction that has a flag that directs the train, and the train flips it in some cases, and

Observability, for one. In the article, the author talks about the Y-junction that has a flag that directs the train, and the train flips it in some cases, and not in others. Being able to see exactly what happens the moment it happens is just immediately comprehendible... there's no "hidden state"; so if it does something unexpected, you can see the whole situation.