There is a popular expression today, "think outside the box". Reviewing the work of Einstein, he analyzed time from a coach class train car, the energy of a photon in confinement, and inertial effects within an elevator. Considering his success, should the motivational speakers reconsider their advice?
There are unresolved issues concerning inertia and how it should be seen, or understood mathematically. If Mach is right, it's not just about the energy content of bodies, it's about all the bodies in a system.
