What is Grit?

“What is grit, really? It's a word that's been used to describe everything under the sun, but it means something specific: when things get hard, you push harder; when you fail, you get back up stronger; when you don't see results, you don't get discouraged, but you just continue to pound away day, after day, after day, with relentlessness, consistency, heart, and passion -- that's grit.”
― Ben Bergeron, Chasing Excellence: A Story About Building the World's Fittest Athletes