Research papers from all over the world are published in thousands of Science journals every year. The quality of these papers clearly has to be evaluated, not only to determine their accuracy and contribution to fields of research, but also to help make informed decisions about rewarding scientists with funding and appointments to research positions. One measure often used to determine the quality of a paper is the so-called "impact factor" of the journal in which it was published. This citation-based metric is meant to rank scientific journals, but there have been numerous criticisms over the years of its use as a measure of the quality of individual research papers. Still, this misuse persists. Why?