Great Question! I know entrepreneurs who have faulted on both sides of the equation. From my perspective it's easier for the folks on the "not trying hard enough" side self-identify as being so with the help of good advisors, mentors, & peer group. If you don't have that then get them!

The other case is much more difficult. I've seen the most amazing victories snatched from the jaws of defeat that seem nothing short of miraculous. That's what makes it difficult. I've also seen people dig a hole so deep they won't likely get out in less than 5 years and it's truly devastating to them and their families (if they have them). If you are in this spot ask your advisors, mentors, & peer group to be very blunt with you and listen to them carefully, and take notes!