Third, there must be time for word of the innovation to spread. Some new ideas, like telephone answering systems, spread rapidly. Others, like public acceptance of the metric system, take much more time. Second, the group that will adopt the new element must be connected by existing communication channels. Third, diffusion must have adequate time to occur.
Diffusion occurs at different rates for different innovations, so the time for adoption varies.
Fourth, diffusion can only occur when the word spreads among members of some social system. In the diffusion process, some people are innovative and some people are not. In addition, some people will adopt early and some people will adopt later. For adoption to work, all these people must be in the population. Innovators will not adopt if they don't think they are leading the way for a general public that all will accept the innovation.