Okay, but if a person has already decided that they "want" a particular product (probably due to the other effects you describe), to the point that they have go

Okay, but if a person has already decided that they "want" a particular product (probably due to the other effects you describe), to the point that they have gone to an e-commerce website and added the product to their shopping cart — but they haven't decided to buy it at that moment, i.e. haven't checked that cart out yet, even though they've come back to the site several times since then to check on both ongoing sales, and the status of that cart... then what aspect of consumer psychology make them ultimately decide at some point to check out the cart with the item in it? And alternately, what is it that makes them ultimately decide to abandon the cart / remove the item from the cart? FOMO is a good explanation for this, I think. Personally, there'll be times when the only reason I'm buying something now — rather than postponing the purchase indefinitely — is that if I don't, it's going to be out-of-stock for who-knows-how-long. My opportunity to choose to buy it is going to be taken away, and I literally fear missing out on the ability to make the purchase. (See Amazon's "only N left" note under some items.) Also, sometimes, the item will suddenly go out-of-stock without any clear date for resupply — leaving me sad that I "dallied" on my choice to buy it and so did "miss out." If such an item comes back in stock, I'll usually immediately buy it, because I now realize I was taking its continued availability for granted, but no longer can — and so "need" to get it before it goes out-of-stock again.