Define the point where you can take a breather. Map the route between this here now and that there then.
If you can count the steps along the way with confidence, that's good. If you know how you might change direction midway through or even turn back, that's good. If you can decide in advance what cues should compel a change of course, that's good. And if you really believe you'll take that breather when you get to the first predefined goal, that's even better.
But maybe -- like Zeno's paradox of Achilles racing against the tortoise -- you'll never allow yourself to catch up. No matter how long it takes you to reach where the tortoise was, by the time you're there the tortoise will have moved farther on!
Ask people who understand you and your project (and who won't flatter you!!!) what they think.
For me this always comes down to a single question.
Do you know what needs to be done?
If you are aware of the solution and understand how it needs to implemented in its entirety then you aren't trying hard enough.
If you are clueless as to a viable solution however and you are merely going through motions to seem like you are working out a solution, you have bitten of a mouthful!
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!