It’s not an accident that some products catch on and some don’t. When an ideavirus occurs, it’s often because all the viral pieces work together. How smooth and easy is it to spread your idea? How often will people sneeze it to their friends? How tightly knit is the group you’re targeting — do they talk much? Do they believe each other?

How reputable are the people most likely to promote your idea? How persistent is it — is it a fad that has to spread fast before it dies, or will the idea have legs (and thus you can invest in spreading it over time)? Put all of your new product developments through this analysis, and you’ll discover which ones are most likely to catch on. Those are the products and ideas worth launching.

— Purple Cow, New Edition: Transform Your Business by Being Remarkable by Seth Godin