Most of these things are not things like candy or a latte. They're durable items I'm unlikely to buy in the near future. If I buy an 8oz hammer, don't recommend another 8oz hammer. I can see perhaps recommending nails, or maybe a ball-peen hammer, maybe a chisel or punch, but not the exact same item. If it's defective, I'll return and perh get an exchange.
Or I bought socks. "Oh, they must have forgotten they actually wanted 12 pairs, not 8". Ok, remind me in a few months, I might be ready to buy again, but not right after the purchase.
Statistically speaking, a person who just bought an 8oz hammer is much more likely to buy another 8oz hammer than some other random person from the population of people who has never shown any interest in hammers at all.
Sure but I'm going to guess statistically they are more likely to buy something not a hammer than a hammer. Maybe "people who bought a hammer also bought...", or, you bought a hammer and nails, here is a cordless drill. I mean, why would I buy a hammer twice in a row, and after that unlikelihood, a third hammer?
If I were going to buy two hammers, I’d have put “2” in the basket in the first place. That’s the more likely scenario. I mean they are not operating blind in a vacuum. They know what I just bought. We’re not trying to guess against an unknown person with unknown purchasing history.
If you're advertising hammers, and you can isolate a cohort of users statistically more likely to buy hammers than users at large, it would be irrational not to target hammer ads at those users.
Or I bought socks. "Oh, they must have forgotten they actually wanted 12 pairs, not 8". Ok, remind me in a few months, I might be ready to buy again, but not right after the purchase.