Regarding stamina defined broadly as it is in this article: One of my favorite quotes comes from an unlikely source: Mike Tyson.

"I don't care how good you are at anything. You don't have discipline you ain’t nothin. Discipline is doing what you hate but doing it like you love it"

[1] Mike Tyson Fighter's Coldest Quotes Of All Time https://www.youtube.com/watch?v=fz9JUENem78&t=100s