"One might, on the basis of experience, derive a few rules of thumb that, if observed, could make development planning less prone to disaster. While my main goal is hardly a point-by-point reform of development practice, such rules would surely include something along the following lines. Take small steps. In an experimental approach to social change, presume that we cannot know the consequences of our interventions in advance. Given this postulate of ignorance, prefer wherever possible to take a small step, stand back, observe, and then plan the next small move. As the biologist J. B. S. Haldane metaphorically described the advantages of smallness: "You can drop a mouse down a thousand-yard mineshaft; and on arriving at the bottom, it gets a slight shock and walks away. A rat is killed, a man broken, a horse splashes." Favor reversibility. Prefer interventions that can easily be undone if they turn out to be mistakes. Irreversible interventions have irreversible consequences. Interventions into ecosystems require particular care in this respect, given our great ignorance about how they interact. Aldo Leopold captured the spirit of caution required: "The first rule of intelligent tinkering is to keep all the parts" Plan on surprises. Choose plans that allow the largest accommodation to the unforeseen. In agricultural schemes this may mean choosing and preparing land so that it can grow any of several crops. In planning housing, it would mean "designing in" flexibility for accommodating changes in family structures or living styles. In a factory it may mean selecting a location, layout, or piece of machinery that allows for new processes, materials, or product lines down the road. Plan on human inventiveness. Always plan under the assumption that those who become involved in the project later will have or will develop the experience and insight to improve on the design."