Everyone remembers the story of Goldilocks and the three bears. Goldilocks finds a cabin in the woods where there seemed to be three sets of everything.
Three chairs, three bowls of porridge, and three beds.
From Caesar (Friends, Romans, Countrymen) to France's motto (Liberté, égalité, fraternité) triplets are everywhere.
Why? They give a sense of rhythm and are more enjoyable to the reader. They are seen as more satisfying or even funny than other groups of numbers.
The same rule is employed in the business world. Psychologically there's a distinct reason, and it loops back to Goldilocks.
Given three pricing options for a set of dinner plates, one really cheap, one really expensive, and one in the middle, which would you pick?
En-masse, people pick the middle option. Neither too cheap nor too expensive. It's just right.
This is the Goldilocks principle.
This works because people don't want the risk of cheap or expensive options, they want the best of both worlds.
Let's say you're a brand that only has two options. A budget option, and your main product. It would seem pointless to add a third, more expensive option, especially if sales aren't doing well.
Panasonic did this in the early '90s selling microwaves. They added a more expensive option, costing nearly double the budget one. Sales of their main product shot up dramatically, and their market share grew by nearly 60%.
Brands want you to pick the middle option, and they're using psychology to trick you into it.