India, Oct. 20 -- Last Friday, the first thing in the morning, I shopped on Zepto, and did what millions of Indians do. I filled my online shopping cart with everything from diyas, sweets, and several items that I did not really need. An unexpected phone call prevented the culmination of my oniomania, or compulsive buying disorder. As the cart lay abandoned for an hour or so, a notification flashed. "Complete your order now and get 10 per cent off + free gift." Of course, I followed the instructions with glee, and happiness, and shopped a bit more.

But this article is not about my buying mania, or oniomania in general. It is about Zepto's nudge which, incidentally, was not random, coincidental, or lucky. It is, in fact, a part of a tacti...