Forrester's book-length explanation of his World2 model that would later be scaled-up by the Limits to Growth group (Meadows, Meadows, and Randers) as World3. Forrester's model is relatively simply, employing some half-dozen levels, including population, pollution and capital investment, but serves the purpose of using system dynamics as a technique to forecast how physical limits will shape the world's socio-economic growth projections. The greatest conclusion Forrester leaves his readers with is that though there is wide agreement for which leverage points in a system are most effective in shaping system behavior, to attain a specific system outcome often require shifting that leverage point in the counterintuitive direction. For example, commonsense would suggest that population control policies would delay the point when the global system reaches its limits, but his model indicates that such policies are effective only in the short run. In time, support for continuing these policies lessens under the belief that a sufficient effort has been made. Other influences such as capital growth, material standard of living, and food availability overrun any short-term gains made by these policies and the system is back on track to slam against physical limits once again.