nonlinear interactions almost always make the behavior of the aggregate more complicated than would be predicted by summing or averaging.

Model building is the art of selecting those aspects of a process that are relevant to the question being asked. As with any art, this selection is guided by taste, elegance, and metaphor it is a matter of induction, rather than deduction. High science depends on this art.

When a new building block is discovered, the result is usually a range of innovations.

Unwrapping occurs when the solution is explicitly built into the program from the start.

The multiplier effect is a major feature of networks and flows. It arises regardless of the particular nature of the resource, be it goods, money, or messages.

The measure of performance of any given agent is the amount of money it accumulates through its actions.

The recycling of resource by the aggregate behavior of a diverse array of agents is much more than the sum of the individual actions.