One frequent saying in innovation circles is "an idea ahead of its time." What a strange phrase. How can an idea be ahead of its time? How can anything be ahead of its time? It makes no sense. What people mean when they say this is one of two things: they think the idea is cool but not necessarily good, or they're trying to get you to buy it. But it's a lousy pitch. How often do the things we imagine from the future work out in the present? Personal rocketships? Cars that fly? Nuclear-powered everything? The odds of cool ideas from sci-fi movies gaining adoption are poor, and it's far from a compliment to have something labeled "ahead of its time."  People don't slave away on insanely difficult work, sacrificing the pleasures of life, with the singular hope that, on their deathbeds, after everything they've done has been ignored, they will be told they were "ahead of their time." To be told your idea is ahead of its time is innovation pity, not praise.
But more importantly for us, this phrase exposes myths about how innovations do gain adoption in the world. First, it assumes technology progresses in a straight line (as covered in Chapter 2). To be ahead of its time implies than an idea has a time, marked in red at the universal innovation headquarters, waiting for people to catch up to it: an entirely inaccurate, innovation-centric view of how people live.
Many technologists think that advantageous innovations will sell themselves, that the obvious benefits of a new idea will be widely realized by potential adopters, and that the innovation will therefore diffuse rapidly. Unfortunately, this is very seldom the case. Most innovations in fact diffuse at a surprisingly slow rate. 
The book takes an anthropological approach to innovation, suggesting that new ideas spread at speeds determined by psychology and sociology, not the abstract merits of those new ideas. This explains the mysteries of great innovations that fail and bad ideas that prevail—there are more significant factors than the ones inventors focus on. Technology prowess matters much less than we think in the diffusion of innovation.
Relative advantage. What value does the new thing have compared to the old? This is perceived advantage, determined by the potential consumer of the innovation, not its makers. This makes it possible for a valueless innovation—from the creator's perspective—to gain acceptance, while more valuable ones do not. Perceived advantage is built on factors that include economics, prestige, convenience, fashion, and satisfaction.
Compatibility. How much effort is required to transition from the current thing to the innovation? If this cost is greater than the relative advantage, most people won't try the innovation. These costs include people's value systems, finances, habits, or personal beliefs. Rogers describes a Peruvian village that rejected the innovation of boiling water because of cultural beliefs that hot foods were only for sick people. You could argue all you wanted about the great benefits of boiling water, but if a religious or cultural belief forbids it, you're wasting your breath. Technological compatibility is only part of what makes an innovation spread: the innovation has to be compatible with habits, beliefs, values, and lifestyles.
Complexity. How much learning is required to apply the innovation? If a box of free, high-quality, infinite battery-life cell phones (and matching solar-powered cell towers) mysteriously appeared in 9th-century England, usage would stay at 0%, as the innovation requires a jump in complexity that would terrify people ("They're witches' eggs—burn them!"). The smaller the perceived conceptual gap, the higher the rate of acceptance.
Trialability. How easy is it to try the innovation? Teabags were first used as giveaways so people could sample tea without buying large tins, radically improving the trialability of brewed tea.  Samples, giveaways, and demonstrations are centuries-old techniques for making it risk-free to try new ideas. This is why the GAP lets you try on clothes, and the Honda dealership gives anyone with a pulse a test-drive. The easier it is to try, the faster innovations diffuse.
Observability. How visible are the results of the innovation? The more visible the perceived advantage, the faster the rate of adoption, especially within social groups. Fashion fads are a great example of highly observable innovations that have little value beyond their observability. Advertising fakes observability, as many ads show people using a product, say, drinking a new brand of beer, with all kinds of wonderful things happening. Many technologies have limited observability, say, software device drivers, compared to physical products like mobile phones and trendy handbags, which people use socially.
This list clarifies why the speed at which innovations spread is determined by factors that are often ignored by innovators. They grow so focused on creating things that they forget that those innovations are good only if people can use them. While there's a lot to be said for raising bars and pushing envelopes, breakthroughs happen for societies when innovations diffuse, not when they remain forever "ahead of their time."
This list is a scorecard for learning from past innovations, as well as a tool for improving diffusion of innovations in the present. The key is to trivialize this list as bastardized marketing, as if these traits can be grafted to an innovation after it's finished, or simply pumped into sales literature and advertising (though those efforts rarely make the difference). Is it a successful innovation if it's purchased but ignored or bought and soon returned? A better way to think of the list is as attributes of the innovation itself.
And since these factors vary from culture to culture, some innovations gain acceptance in surprising ways. There is no uniformity in progress around the world; innovations may be adopted by one culture or nation decades before another. As William Gibson wrote, "The future is here. It's just not widely distributed yet," and no innovation is immune. Everything new passes through groups of people in unpredictable ways and, given the limits of human nature, always will.
 Notice I said movies, not sci-fi books. Films are visual media and choose technologies that look good or have dramatic value, not necessarily things that solve important problems, have progressive value, or obey the laws of physics.
 Everett M. Rogers, Diffusion of Innovations (Free Press, 2003), 15.
 Joel Levy, Really Useful: The Origins of Everyday Things (Firefly Books Ltd, 2002).