KE compared to mass equivalent at low speeds

An object is moving at ordinary nonrelativistic speeds. Compare its kinetic energy to the energy mc² it has purely because of its mass.

The speed of light is a very big number, so mc² is a huge number of joules. The object has a gigantic amount of energy because of its mass, and only a relatively small amount of additional kinetic energy because of its motion.

Another way of seeing this is that at low speeds, γ is only a tiny bit greater than 1, so E is only a tiny bit greater than mc².