As a thought experiment along the lines of Merlin Mann’s interesting 5ives.com site, I thought I’d take a stab at listing five things that, as a designer, I don’t know anything about.
(Admissions are all the rage these days—Tom Cruise eating placenta, Donald Trump getting paid for baby photos, former White House administrators calling out their boss, etc.—so why not.)

1. How color settings work best in Photoshop.
2. How browsers technically render HTML markup.
3. Whether it’s actually easier to read sans serif type online.
4. Why the color purple is rarely used as a link color even though, early on, it was determined that purple links are the default “visited” state.
5. Why the American flag, in its design perfection, actually looks like the United States.