Most effects in psychology are relatively unimportant. That is, most variables, considered in isolation, have relatively little impact on behavior. This doesn't mean... that we should all abandon psychology and become plumbers instead. The small magnitude of most effects in psychology is itself a discovery of psychology. One might argue, in fact, that it is one of the great metadiscoveries of the field. Most variables have little impact, and thus most of the phenomena studied by psychologists are products of a multiplicity of variables.

(p. 251) - The Ape that Kicked the Hornet's Nest (2013)