While that's true, it's beside the point. In this case, it's all about finding and formulating the problem. The solution is the easier bit. Consider this - how

While that's true, it's beside the point. In this case, it's all about finding and formulating the problem. The solution is the easier bit. Consider this - how many of us have crossed off "m" on both sides of m d^r/dt^2 = -GMm/r^2 without actually noticing the problem with that? We're equating "mass" as associated with inertia and "mass" as associated with producing the gravitational effect. This is the central point from which pretty much all of GR emerges.