In this paper, first, we will discuss the importance of physical insight in computational electromagnetics. We explain why it is relatively easy to arrive at fast algorithms for static problems, but harder for wave physics problems. Second, the understanding of wave physics is very important in classical electromagnetics, but its understanding also allows us to understand other physical phenomena requiring wave physics, such as transport of electrons in complex structures. Last, we discuss the Casimir force calculation that needs a combine understanding of statistical physics, quantum electromagnetics, and classical electromagnetics. Computational electromagnetics can play an important role in Casimir force calculation.