The quotation "Every heart vibrates to that iron string" is part of a passage from "Self-Reliance," which is an essay penned by Ralph Waldo Emerson. Published in 1841, the dissertation delved into the relationship between an individual and society.
Emerson was one of the leading figures of New England Transcendentalism, which was a movement proposing that true knowledge is derived from within a rational and acting person rather than from the external teachings imposed by society. In "Self-Reliance," Emerson emphasized the importance of cultivating the value of self-independence in the face of an often authoritarian society. Personal realization can only be achieved if the individual identity of a person is not lost to the norms and standards of society.