This proverb comes from a poem by Uesugi Youzan (上杉鷹山), from back in the Edo period. It’s pretty cool and being a Japanese poem isn’t so long, so here’s the full text.

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.