One of my favorite products at Warby Parker also happens to be our worst-selling item: the monocle. When we launched in 2010, our debut collection featured 27 pairs of eyeglasses and one monocle--a handsome tortoiseshell model named after Colonel MustardDespite dismal sales and growth prospects that roughly equal zero, the monocle has remained in rotation ever since. My wife Rachel even waged a bet with my co-founder Jeff that we'd never sell out of our first order.

Her skepticism made sense. On its face, a monocle is a strange item for a 21st-century company to sell. It seems like the equivalent of Apple unveiling an iTypewriter or Schwinn manufacturing a penny-farthing bicycle (the kind with the gigantic front wheel). Or SanDisk rolling out a line of floppy disks. In general, obsolete technology is obsolete for a reason. Monocles are no exception.

But that's exactly why I love it. Nobody expects to stumble across a monocle while shopping in 2013. We have a showroom right inside our office headquarters in New York, and one of my favorite things to do is catch sight of customers discovering the monocle. A familiar behavioral arc follows: it starts with a "What the hell?" expression, proceeds to a smile, and usually ends with trying on the monocle, forcing various companions to try on the monocle, imitating a historical figure, and/or snapping a picture. 

The truth is that the monocle creates a sense of surprise in customers while maintaining an intuitive connection to our core products--which is an important distinction to make. It's not a random gimmick. We could sell fly-fishing rods or bean bags and provoke an equally surprised response, but it would also be a mystified response. The goal is to surprise customers, not confuse them. 

The monocle is also a succinct and quirky way to represent what Warby Parker stands for--in other words, a brand piece. It's unexpected, it starts conversations, and it's fun to share. (Where else can you buy a monocle?) And because it lives entirely outside any remotely relevant trend cycle, it's also, in its own peculiar way, sort of timeless. A handful of chefs have even told me that they use the monocle in their restaurant kitchens to read recipes; it's easy to store in a pocket and doesn't fog up as easily as glasses. I think of it as our own version of the stick of gum that used to come in packs of baseball cards--a small gesture that sets the brand apart.

My wife still owes Jeff ten dollars.