In Alexander’s experience, the winds randomly changed direction from day to day. Over the course of a week or two, one was very likely to encounter a favorable wind. It’s not one random variable, it’s more like one independent random variable per day.
Also, although I didn’t discuss it in the OP, the book argues that a large premodern army sitting in one place would quickly exhaust nearby food stores. That was probably also a large factor in Alexander’s decision to leave India; turning back would likely have left them in a tough spot within a couple months.
In Alexander’s experience, the winds randomly changed direction from day to day. Over the course of a week or two, one was very likely to encounter a favorable wind. It’s not one random variable, it’s more like one independent random variable per day.
Also, although I didn’t discuss it in the OP, the book argues that a large premodern army sitting in one place would quickly exhaust nearby food stores. That was probably also a large factor in Alexander’s decision to leave India; turning back would likely have left them in a tough spot within a couple months.