Angela Duckworth in her book Grit: The Power of Passion and Perseverance, states that passion and perseverance, i.e. our excitement about something and our commitment to pursuing it, are the fundamentals for grittiness.
She makes a cogent case for the power of grit in yielding success and that—like your errant six-pack abs or my personal fave, the deep V created by tight lower oblique muscles—you can develop your grittiness.
As with many of these theories, it’s always nice to read that we have a modicum of control—we can work on cultivating grit by actively engaging in practices to strengthen that muscle.
You can develop your grit!