「為せば成る
為さねば成らぬ何事も
成らぬは人の為さぬなりけり」

Naseba naru
Nasaneba naranu nanigoto mo
Naranu wa hito no nasanu nari keri

"If you try, you may succeed.
If you don't try, you will not succeed. This is true for of all things.
Not succeeding is the result of not trying."

This is from Uesugi Harunori, a famous and exemplary daimyo (Japanese feudal lord) from the Edo era (the historical period between 1603 and 1868; he lived from 1751 to 1822).

Although he is well known for applying a lot of financial reforms and politicies that saved the Yonezawa province from hunger and poverty, this poem is the teaching that stuck with the Japanese people as an example of self-discipline.