Whenever I get to feeling like this, one of my go-to pick-me-ups is Rudyard Kipling's Poem, "If." There's a version of it read by Michael Caine. The bit that gets me is:
"If you can meet with triumph and disaster,
"And treat those two imposters just the same;"
"If you can meet with triumph and disaster,
"And treat those two imposters just the same;"