Grit is just one quality of a good executer. Grit with poor execution doesn't yield results. Grit is not the secret to success, execution is.
It is extremely rare to see an actual individual being really successful. Most of the time, they are or were part of a company. This is because a person can only devote so much time and skill into anything.
And making the right connection is a matter of place (Ivy League anyone?), time (gold rush is good, recession is bad), interpersonal skills and finally luck.
There are many exceptions to this rule that make this difficult (born into poverty or third world country, etc) but the great majority of people who complain, at least in the US, spend their evenings at happy hours and their weekends at the football game. You can't do that and then blame it on luck or bad circumstance. I work with hundreds of "entreprneurs" that spend weeks and months obsessing over logo design and color and UX, when they have zero customers at their door. Execution is a skill, it can be learned, and 99% of people just don't have it.