Tenacity. It's a powerful word. For much of my life, the word has meant going after what I want until I get told "no," or until I realize it's not going to work, or until I get tired of beating my head against a wall. Then, tenacity means, "Eh...never mind...I'll just do something else."
It doesn't really do justice to the word. Pure and simple, tenacity means, "I'm going to do this thing or I'm going to die trying to do it....and death is not an option."