In 2002 the psychologists Edwin Locke and Gary Latham reviewed their research on goals in American Psychologist. The article was subtitled “A 35-Year Odyssey.” “We found that specific, difficult goals consistently led to higher performance than urging people to do their best,” they wrote. They added: “when people are asked to do their best, they do not do so.”
The reason, they explained, is that “do-your-best goals have no external referent and thus are defined idiosyncratically.” This “allows for a wide range of acceptable performance levels, which is not the case when a goal level is specified.” The findings covered “well over 100 different tasks involving more than 40,000 participants” in “at least eight countries.”