How do you identify something as ephemeral as the product zeitgeist fit? Here are four tests to spot it in the wild.

• “Nerd Heat”: Coined by my partner Chris Dixon, this is when the most talented, hardest working, and most in-demand people—the product managers, engineers, and data scientists—are so intrigued by a product that they’re working on it, excited by it, and trying to make it a thing.here’s a good chance that they’ll eventually make it happen, moving it beyond the fringes to the mainstream.
• The “Despite Test”: When people are using a product despite the fact that it’s not the best thing out there, or, in some cases, that it’s straight-up terrible (see examples above), it’s a great sign. It shows that the product has a line into something emotional, not solely functional. Wanted, not just needed.
• The “T-shirt Test”: If people with no connection to the company are wearing their t-shirts or putting their stickers on their laptops or wearing their socks, that desire to associate with the idea indicates as much a movement as a product.
• The “Eyebrow Test”: In the early days, things that have product zeitgeist fit often feel misunderstood or controversial. At first blush, the conceit may even raise a few eyebrows. But to the people who have been working on those products, they’re so clearly elegant, if temporarily imperfect, solutions to big and important problems that they seem almost obvious once they recognize it.