Like Rachylou, I'm wary about speakers who propose a universal answer to complex issues. Perseverance, optimism, resilience, support, and, yes, "grit" as the speaker chooses to call it--can be important in many contexts, but I'm not sure they are any more vital than stubbornness, calculated submission, rebellion, or distancing--or any other quality we choose to tease out of human behaviour. I am fairly sure my promoting any of those latter qualities in our children, though, wouldn't lead to a $$$ speaking engagement or a snappy saying in popular media.
After spending half a century working with children and adults in a classroom, all I can say is that I truly don't know why some keep moving while others stop. And, even if I did have the answer, why is movement, instead of stillness, automatically preferable? What is it we are moving towards--Spiritual transcendence? Monetary success? Intellectual curiousity? Mindfulness? Social compatibility? High test scores? Celebrity? Are "grit", patience, and head-down perseverance always the right tools to use. Does a focus on forward momentum displace the benefits we could get from reflection and diversion. And, even if we accept forward momentum as the "right" answer, couldn't a series of sprints, with breaks for rest and re-calculation, keep us more alert and mobile in an unfriendly or unpredictable environment? If we can't agree on what we are aiming towards, how in world can we know how what qualities are necessary to "teach" another person? And, are these qualities even "teachable" or do they come as by-products of self-awareness and experiences--pleasant and unpleasant.
Complicated stuff, despite so many experts wanting to give me the answer. I keep thinking maybe the only person who can judge the success of my life is myself, which leaves me to be the only one who can figure out what I need to do to get there. It's a tough lesson to teach a child, though.