Perhaps a Siamese twin of tenacity,
Evidently a brother to perseverance;
Resolve to fight on when hardest hit,
Stubbornness informed by a goal of importance;
Innate determination to stay at it;
Something queer that clings to non-existence hope
That cynics will swear by all that it’s vain;
Earnest, ever revving urge to raise the scope
Neither skeptics nor discouragers can assail;
Casting off the all obvious signs of doom and fate;
Erring but believing in gradual climb and scale.

Hannington Mumo

http://www.poemhunter.com/poem/persistence-8/