Sufficient incentives for people to do all the necessary learning. Sufficient incentives for people to pass on the learning to a handful of others. A feedback and checking mechanism for making sure the chain reaction stays on target, both in the individual and in the group as a whole. While these mass-produced forms of teaching have obvious economic payoffs for a few people, they have many shortcomings when compared with a chain reaction approach in which one person supports a handful of others, either individually or in a small group. A chain reaction that includes an ongoing support structure will cause a greater amount of learning.
Chain reactions are relatively inexpensive since very little infrastructure is needed.
In other words, you don't need to pay for buildings, mass advertising, or for building a large distribution network. Because little infrastructure is needed, chain reactions are easily translated into other cultures, languages, and can help people with little resources. Chain reactions can rapidly grow. Chain reactions do have some disadvantages, and that is why they are not as common as mass-produced learning situations. At the beginning they grow more slowly than mass-produced learning.