 As Hecht has emphasized, Einstein never wrote down his famous result using the symbols “\(E\)” and “\(m\)” as they appear in the famous equation attributed to him (Hecht 2012). Although part of the reason is merely that Einstein used different letters for energy, mass, and the speed of light in his early papers discussing mass-energy equivalence (in 1905 and 1906), deeper reasons related to how we should understand the result quickly emerged. 