I think we should, in our studies of the human interaction, look at the concept of social inertia. Inertia as it applies in physics is an object's resistance to change. For example, the rolling ball. The faster it is rolling, the more it "wants" to stay rolling, thus making it harder to stop. Social inertia applies this concept to human behavior. Humanity ingrained in a rut will tend to want to stay in said rut. The more ingrained they are, the harder it will be to create a new rut. This concept gets right to the heart of one of our problems in development: Once we develop the basis, how do we go about making it happen? In the Foundation series, the Second Foundation was largely responsible for the Seldon Plan staying on track. They subtlely manipulated the masses where necessary to make sure the Plan stayed on track. Developing the equations, flowcharts, sets, whatever, is one thing. Making them happen is something else entirely.

This is definitely an important concept. Because people continue to act on a course plotted by previous actions, they accelerate this inertia. The positive feedback loop is a very simple explanation of the same thing. This implies that a single action may not always be enough to effect a trend, constant force must be applied for a period of time in order to decrease the acceleration. This constant force may be started by a single action, however, if a select group of society is changed by it and thereby plots to strengthen it (unknowingly, perhaps). This group, however, being only a minority, must achieve greater accelerative force in order to grow, somehow shift the majority, and thereby change the original societal inertia.
Alternatively, what if some roadblock was placed in front of the inertia, something of such great force that the change would be nearly instantaneous? This would probably be related to something external affecting the society, such as an intervening, stronger society, but history I think shows that sudden actions only increase suffering. Therefore, we can conclude that excellence in psychohistory involves great patience, and subtlety. We must learn to overcome negative social inertia through a small but constant pressure (and one in the right direction!).