Do not pity the weakness of a foe because when he gains strength he will not spare thee.
Boast not of thy moustaches when thou seest thy foe is weak.
There is marrow in every bone, a man in every coat.
Saadi Shirazi
http://www.poemhunter.com/poem/ch-08-on-rules-for-conduct-in-life-admonition-09/