The figure above illustrates the correlation between two variables, let us say success and ability. Each point represents an individual whose level of success and ability are shown on the vertical and horizontal axes, respectively. In the figure, the correlation is high, but not 100%.
For example, in American football the ability axis might represent the quantities obsessively tracked by NFL scouts: sprinting speed (40 yard dash time), natural strength (bench press), etc., while the vertical axis represents actual output, like passes caught or rushing yards gained. In real life, output is never purely determined by a single, or even several, input ability or abilities. If nothing else, luck ensures that the correlation is imperfect. Sports fans know that the fastest wide receiver isn't necessarily the best, nor the tallest basketball center the most productive, even if being fast or tall confer specific advantages. In the figure, the most able individual is not the most successful. They are seldom the same individual unless the correlation is 100%
In science or academia, we might take the horizontal axis to represent raw intellectual ability. The graph tells us to expect that the smartest person is not necessarily the most successful. It also suggests a population of successful but insecure people (the upper right dots above the fit line -- they are dumber than peers of similar accomplishment) and a population of smart people who are bitter about their unrecognized genius (dots on far right below the fit line -- they are smarter than peers of similar accomplishment).
