  People are influenced by the choices of others, a phenomenon observed across
contexts in the social and behavioral sciences. Social influence can lock in an
initial popularity advantage of an option over a higher quality alternative.
Yet several experiments designed to enable social influence have found that
social systems self-correct rather than lock-in. Here we identify a behavioral
phenomenon that makes inferior lock-in possible, which we call the 'marginal
majority effect': A discontinuous increase in the choice probability of an
option as its popularity exceeds that of a competing option. We demonstrate the
existence of marginal majority effects in several recent experiments and show
that lock-in always occurs when the effect is large enough to offset the
quality effect on choice, but rarely otherwise. Our results reconcile
conflicting past empirical evidence and connect a behavioral phenomenon to the
possibility of social lock-in.
