Any attempt to shape the world and modify human personality in order to create a self-chosen pattern of life involves many unknown consequences. Human destiny is bound to remain a gamble, because at some unpredictable time and in some unforeseeable manner nature will strike back. The multiplicity of determinants which affect biological systems limits the power of the experimental method to predict their trends and behavior.

Eradication of microbial disease is a will-o'-the-wisp; pursuing it leads into a morass of hazy biological concepts and half truths.

Social evolution may be the result of intention, but it rarely, if ever, produces the result intended.

...Search for the cause may be a hopeless pursuit because most disease states are the indirect outcome of a constellation of circumstances.

Sometimes the more measurable drives out the most important.

As long as mankind is made up of independent individuals with free will, there cannot be any social status quo. Men will develop new urges, and these will give rise to new problems, which will require ever new solutions. Human life implies adventure, and there is no adventure without struggles and dangers.

To ward off disease or recover health, people as a rule find it easier to depend on healers than to attempt the more difficult task of living wisely.