In 1974, Joe Henderson, then editor of Runner's World magazine, published his now classic book Run Gently, Run Long. In this book and his other writing, Henderson advocated running gently in order to be able to run long distances. Aspects of gentle running include such things as: long slow distances, easy rest/recovery days, and limited racing.
This philosophy has guided my running for the intervening three decades. I don't have much natural speed, so I run long slow distances rather than short fast sprints. I take at least one rest day and a couple short easy days per week. I limit my racing or fast runs, so that most of the miles I run are at a comfortable pace.
When I first read the book in my early twenties, I interpreted "run long" solely in terms in the length of individual runs. By running slowly and gently, I could run enough miles to complete marathons and fairly frequent training runs of comparable and longer distances.
In middle age, I came to see "run long" more in terms of a lifetime of running. Sometime this fall - I forget the exact date - will mark the 40th anniversary of my first run, not counting the running play that kids do naturally. Running gently has allowed me to keep running for forty years.
Taking regular rest and recovery days, running plenty of slow easy miles to balance the hard racing miles, giving injuries a chance to heal, and other aspects of gentle running have kept me from burning out on running. I no longer run as fast or far as in my youth, but I am still running. I hope to keep these old legs moving, however slowly, until I cross life's final finish line.
This philosophy also worked for Joe Henderson. He is still running and writing about it in his 60s.
A lifetime of running gently allows a lifetime of running long.