An element of effort and straining exists in the word attention itself, which comes from Latin ad + tendere, “to stretch toward.” This relationship finds one of its most compelling expressions in William James’s 1890 The Principles of Psychology. Defining attention as the ability to hold something before the mind, James observes that the inclination of attention is toward fleetingness. He quotes the physicist and physician Hermann von Helmholtz, who had experimented on himself with various distractions:
