Amazon is not an idiot:
> You need two insights here:
> 1) Conditional probability is a mathematical technology that does exist.
> 2) Buying X is not entirely random across the population.
> The ways X is not random vary based on the good [math]. Consider refrigerators.
> You probably buy one every ten years. If I don't know where you are in your refrigerator cycle, my prior estimate should be 2.7e-4 probability of you buying it tomorrow.
> Suppose I know you bought yesterday. In my life on earth, I have realized that buyer's remorse is a thing.
> What's a SWAG for how often a purchase immediately goes wrong? Not right color? Fridge DOA? Shoot I mismeasured my kitchen? Wife just hates it? Call that 2%. If I fix it within a week, then 2% / 7 = 2.9e-3 probability of purchasing a new fridge.
> That's a 10X relative risk.
Source: patio11 (Patrick McKenzie)