I first heard these lines when I was in high school Studying Julius Caesar in English class but the words have proven to be my mantra for life.
"Cowards die many times before their deaths;
The valiant never taste of death but once."
Every time catch myself worrying in vain about future events that I can neither predict nor control, these lines remind me not to be a coward. We spent a whole year studying this play and our English teacher was one of those who changes the lives of their students. The impact of the play or Mr. J's teaching of it would not be apparent to me until a good decade later when I first came into contact with significant real-life difficulties.
People find solace in reciting mantras in times of trouble, meditating or praying in silence. The words of Caesar as imagined by Shakespeare have served me just as well. I may not be quite as "valiant" as I would like but it helps to have these words play in my head each time I fail to live up to my own expectations as a human being.