It's tightly structured, which I love to read again and again. 'Fortitude' is the last word of each stanza. 'Pain' and 'know', two words that link up to show your theme, are emphasised as identical rhymes, which also lets you use the word twice in different ways. Learn/earn and meant/spent are beautifully linked in their meanings. The freely composed metre gives speech-rhythms that are just appropriate to what is being said.
You didn't say much: just a proverb that most people come up with sometimes. But actually this is the most important type of poem, putting an ordinary thought in memorable words.