Pertinacity is a quality of sticking with something, no matter what. It's a type of persistent determination.
People who have pertinacity won't give up, and they stick with things doggedly. Pursuing a difficult career requires pertinacity. Pertinacity is a mix of courage, conviction, and a little stubbornness. Pertinacity requires a strong will and self-confidence. Pertinacity can also be called perseverance, persistence, and tenaciousness. Pertinacity is related to the word tenacity, which is also a quality that combines determination and commitment.