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.

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.

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

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.