“don’t overdo it. underdo it. you aren’t running because you’re in a hurry to get somewhere. it’s your choice of whether to run to punish your self or to experience your self. if you choose, with me, the latter, then every run can be joyful. the key words are, Take it easy!! create your self as a runner gradually, patiently, relaxedly.”
The Zen of Running, by Fred Rohe (1975)
A really really great old book. out of print but easily found at amazon.com used and maybe your library.