Wisdom in distance running is not so much know thyself as it is slow thyself. Set off too fast at the beginning of a race, and you can guarantee to be hurting at the end --- if you even make it that far. When feeling fresh and frisky the temptation to blast along is almost irresistable. Resist.
Likewise in life, when entering any endeavor --- a diary, a diet, a courtship, the study of a language, whatever --- start slowly, at a sustainable pace for the long run.
(see also DeliberateSpeed (23 Aug 1999), ... )