Think of human relationships as entanglements. How do they bind you; how do they reveal who you really are? Daniel Horowitz for NPR hide caption

itoggle caption Daniel Horowitz for NPR

U.S. soldiers at Long Binh base in South Vietnam line up to give urine samples at a heroin detection center before departing for the United States. About 20 percent of soldiers said they were addicts, but most didn't continue drug use back home. AP hide caption

itoggle caption AP

A group of 3,000 ordinary citizens, armed with nothing more than an Internet connection, is often making better forecasts of global events than CIA analysts. Here, a man crosses the CIA logo at its headquarters in Langley, Va. Saul Loeb/AFP/Getty Images hide caption

itoggle caption Saul Loeb/AFP/Getty Images

Having a perfect memory can put a strain on relationships, because every slight is remembered. Katherine Streeter for NPR hide caption

itoggle caption Katherine Streeter for NPR