Noun: Courage and resolve; strength of character.
Verb: Clench (the teeth), especially in order to keep one's resolve when faced with an unpleasant or painful duty.
Resolve defined ...
Noun: Firm determination to do something.
Courage defined ...
Noun: Strength in the face of pain or grief.
Quitting defined ...
Noun: To give up or resign; stop, cease and discontinue; to stop trying, struggling, or the like; accept or acknowledge defeat.
Courage defined again in case you missed it and in regards to quitting ...
Noun: Strength in the face of pain or grief.
Resolve defined again in case you missed it and in regards to quitting ...
Noun: Firm determination to do something.
Grit defined again to drive the point that quitting does not produce grit ...
Noun: Courage and resolve; strength of character.
Verb: Clench (the teeth), especially in order to keep one's resolve when faced with an unpleasant or painful duty.
Application: We succeed and fail all day long. However, failing due to trying is more productive in the grand scheme of our growth trajectory than failing because of quitting.