I disagree with the author's premise that you have "grit" only when it can be applied in any direction. To me, "grit" requires adversity instead of simply overall breadth. It's quite easy for us humans to do something if everything is going well. What about when it's not going well? Do we have enough to persevere through all times, including hard ones? Your startup is failing? Your research is yielding no fruit? You…
Consider two scenarios of a child playing who soccer:
Child 1 hates soccer, but is forced to play by their parents: I see no lack of grit in such a scenario if the child resists going to practices & games and pushes his parents to let him quit.
Child 2 likes soccer and wants to play. However, in their first game they play goalie and the team loses 3 to 0. If the child doubles down and decided to practice more, that is grit. If they get discourages and want to quit, that is a lack of grit.
Obviously there's still more to it than the relatively simple outline here, but it shouldn't be considered a universal ability to do any & everything or never abandon a project.