Motivational Interviewing: Helping People Change by William R. Miller and Stephen Rollnick outlines a technique that doctors, therapists, social workers, and, yes, trainers can use to encourage change. It developed in the context of helping problem drinkers, but has since found many more applications.
What the authors found was that people are usually ambivalent about making changes. Getting those people to make the arguments for change themselves rather than lecturing them produced results. When people consider change and talk about it, they often have a blend of “change talk” and “sustain talk;” in other words, they voice both sides of the question. A skilled listener who wants to help change can encourage the change by drawing out more and more change talk.
There is a lot more to the system, but I found it fascinating to discover such a compassionate and respectful way of evoking positive change.
(Thanks to Carolyn H. for the recommendation!)