Developing grit is linked to all sorts of positive outcomes such as gritty people are more likely to graduate from college, more likely to succeed as a teacher, more likely to make it through US Military Academy at West Point, and many other positive results. Developing grit requires perseverance over a period of time. You can't build grit overnight. Being committed to one activity for multiple years is an indicator of grit.
Kids need to spend time doing things they like but that takes practice. Doing so with a supportive and demanding adult is the ideal condition. Demanding doesn't mean degrading of the child. It means that the adult sets high expectations and holds the kid to those expectation.
In my family's experience, my children are both able to participate in activities. Each of my children participate in athletics and in music/theater. These activities provide an opportunity to practice skills over a long period of time. Whether it is running cross country or acting in a one act play, it takes considerable time and effort to improve in either of these activities. Of course, these activities are fun. That doesn't take away the fact that it takes effort to become better. The fact that they are of interest helps kids stick with it. It appears that ability to stick with an activity as a child will be transferred to other activities as child becomes an adult.
The arts are a core part of what schools should offer. We know that it is good for students to participate in activities so we need to make sure we find ways to ensure as many kids have access to music, arts, and athletics as possible. Unfortunately, access to these activities are not always even for a variety of reasons. When kids are young, you often have to pay to participate in club athletics or learn to play an instrument. Some activites require that you drive your children all around town or require you to travel across the state which become very cost prohibitive for many families. The more we are able to offer these at no costs, the more our society benefits from the development of gritty children. Often times, when looking at what should be cut in schools, the arts take the biggest hit. It is critical that we look at these activities with the value they truly provide students. In schools with high poverty, we should be looking at ways of expanding arts, not cutting them.
"Grit: The Power of Passion and Perseverance" by Angela Duckworth