Even after you’ve sold them on personas, even after you’ve explained that you want to design for a specific persona first, even after you warned them about the perils of the “elastic user,” you can find yourself hearing things like, “Well, I know this guy who would do it this way...”
To help clients who won't be put off by pop-culture references, I reference the parable of The Homer.
For those who aren’t familiar with the Simpsons episode “Oh Brother, Where Art Thou?” (Season 2, Episode 15), it plays out like this: Homer meets his long lost brother Herb, who happens to head an automobile company. Believing Homer to be the perfect “everyman,” Herb instructs his designers to make exactly the car that Homer wants.
If it needs saying, Homer is something of a moron, and the resulting car he “designs” is something like this:
The Homer: Powerful like a gorilla, yet soft and yielding like a Nerf ball (props to Carlos Bisquertt for this 3D model of the cartoon version.)
As you can imagine, this monstrosity that features tail fins, bubble domes, shag carpeting, and multiple horns that play “La Cucaracha,” ruins Herb’s company.
The moral is of course that designing for almost any single individual runs a huge risk of building a product around personal idiosyncrasies — the things that are different about that person, which is a lot different than designing for personas or user archetypes where the goal is to make decisions focused on the commonalities between members of the intended audience.