Personalization work but companies tend to overfit which reduces the benefits of personalization.

Let’s forget the obvious demographics correlation with products and just start with an example.

Simply knowing that someone is active on HN, I wills bet ads on tech product and services would be more effective on them compared to a random person on the internet. The problem comes when the personalization gets too personal and stuck in the past, like how Amazon recommends another of the same product category after you bought one.