The United States education system must improve its ability to produce scientists, engineers, and programmers. Despite numerous national, state, and local efforts to make the study of STEM (science, technology, engineering, and mathematics) subjects more fun in K-12, initial interest in those subjects drops off precipitously in middle and later high school and college. The author presents some explanations for this decline and argues that the emphasis on fun is misplaced, as is, more generally, the emphasis on intrinsic rather than extrinsic motivators to study STEM. STEM subjects inevitably become difficult, which requires grit and is not compatible with an expectation of continual enjoyment. Extrinsic motivators such as success, respect, and social utility are valid and powerful. In addition, the national-level motivations for promoting more STEM in the first place are extrinsic, so that the current K-12 over-emphasis on fun at the individual level is inconsistent as well as insufficient.