This is so hard to get right. Even with a lot of data, I am a frequent shopper at Amazon for instance, you cannot predict my needs when they are always different. I may be shopping for a gift, something I would never by for myself, and then a year later still get recommendations based on that. For me the main reason to leave a cart, having to pay for shipping, shipping that takes too long, or a coupon that at checkout has unexpected restrictions. A spot-on recommendation wouldn’t make me change my mind.