Quote Originally Posted by Millstone85 View Post
Monks are also big on meditation and putting one's body, mind and spirit in harmony. It is not far fetched to interpret the psion as using the same inner energy, only with greater focus on the mental than on the physical.
In 5e (I can't speak for other editions) Ki is magic that flows through living bodies, which puts it on a more physical than mental level. It also avoids any weirdness in multiclassing.