6 ideas
Members of a social system adopt an innovation at different times, falling into five categories based on innovativeness: innovators, early adopters, early majority, late majority, and laggards. When plotted over time, adoption follows a normal bell curve, and the categories are defined by standard deviations from the mean adoption time.
An innovation's speed of adoption is predicted by five perceived attributes: relative advantage (is it better than what it replaces?), compatibility (does it fit existing values and needs?), complexity (is it hard to understand?), trialability (can it be tested in small steps?), and observability (are results visible to others?). Innovations scoring high on advantage, compatibility, trialability, and observability and low on complexity diffuse faster.
Certain individuals exert disproportionate informal influence over others' attitudes and behaviors because they are central, respected, and conform closely to group norms. Diffusion accelerates when change agents target these opinion leaders rather than addressing all members equally, because their endorsement legitimizes adoption for the rest of the network.
An individual moves through a sequence from knowledge (awareness), to persuasion (forming an attitude), to decision (adopt or reject), to implementation (actual use), to confirmation (seeking reinforcement of the choice). Each stage requires different information and can produce rejection or later discontinuance, so interventions must match the stage the person is in.
People tend to interact with others similar to themselves (homophily), which makes communication easy but limits exposure to novel ideas. Diffusion across a system therefore depends on bridging contacts between dissimilar people (heterophily), even though such links are harder to form and feel less comfortable.
A health worker spent two years trying to get a Peruvian village to boil drinking water, succeeding with only a handful of households. The campaign failed because boiling water was culturally associated with sickness and the innovation conflicted with local beliefs, demonstrating that incompatibility with existing norms blocks adoption regardless of objective benefit.