Thoughts on marathon training?

A poem by my late colleague Kenneth Koch, "You Want a Social Life, with Friends," courtesy of Josh Glenn:

You want a social life, with friends.
A passionate love life and as well
To work hard every day. What's true
Is of these three you may have two
And two can pay you dividends
But never may have three.

There isn't time enough, my friends--
Though dawn begins, yet midnight ends--
To find the time to have love, work, and friends.
Michelangelo had feeling
For Vittoria and the Ceiling
But did he go to parties at day's end?

Homer nightly went to banquets
Wrote all day but had no lockets
Bright with pictures of his Girl.
I know one who loves and parties
And has done so since his thirties
But writes hardly anything at all.