Unless a person has a disordered problem with online shopping, wanting quick delivery is not a problematic example of instant gratification. And because of free return policies, consumers often buy an item with the understanding it might be sent back, which means they aren’t even committed yet to the purchase.

The same year Amazon Prime started, only 46 percent of Americans had ever bought a product online. Thus, prompt delivery didn’t stem from consumers’ demand for instant gratification. It came from a retailer’s demand for consumers.

When a person perceives pleasure say, a glimpse of a chocolate cake on a restaurant’s dessert menu, the ventral striatum experiences increased activity. The prefrontal cortex, which handles reasoning and rational thought, must override the drive and tell the server ‘just the chec...