For me, it is a Winston Churchill quote: “Never, never, never give up.” That has meant quite a lot to me throughout most of my life (well, at least since high school, when I first read it!).
It has helped through struggles in college – I held on to it as I moved on from engineering (definitely not me) to computer science.
It has helped through relationship difficulties – I never gave up hope that a decent person was out there for me. Sure enough there was – and we’ve been married for 21 (almost 22) years now.
It has helped me through struggles with my daughter’s seizures, the years it took to get a diagnosis, and the struggle to accept what cannot be changed. (And it continues to help with that, of course).