Well, they can still take the donut and then go to the gym out of guilt :)
Now seriously, let’s say you manage a platform telling someone there is “Only 1 ticket left” for a trip they’ve been dreaming about and they’re going to get a good deal if they act now and they take it even if they told you earlier they’re short on money and they go and have the trip of their life. Isn’t this the same thing but with a positive outcome and the greatest use of scarcity? What I mean is that what Tristan Harris said can go both ways.
And funny enough, I do stand by my mug because in the end I still like stainless steel and coffee :) This won’t change with a purchase, whether it’s a bad or good one.