In our technologically advanced society proficiency in mathematics is paramount to success in the science, technology, engineering, and mathematics (STEM) employment sector. Mathematics anxiety negatively affects an individual's physiological and cognitive functioning, which results in the individual obtaining lower achievement in mathematics. The consequences of low mathematics achievement can have devastating consequences for the individual's career in STEM fields which require high level mathematics. This article will provide a review of the prevalence of mathematics anxiety, its historical development, as well as theories from education, psychology, neuroscience and causal factors purporting to provide a comprehensive understanding of mathematics anxiety. We propose a fourth causal factor, missed opportunity, in which the individual is high functioning academically, but exhibiting mathematics anxiety. He or she is not able to perform well in mathematics due to missing the opportunity to learn the foundational mathematics knowledge necessary in STEM fields.