Everyone from Winston Churchill to Nike will tell you to never, never give up. Just do it. Perseverance and stick-to-itness are often held up like magic success wands. But sometimes, quitting is smarter. Some projects turn into such productivity drains that they drive you rather than the other way around. Others spin out of control. Your tenacity starts to take more out of you than it gives back.

If you’re stuck in a project like that, you’re doing yourself more harm than good by sticking with it. Maybe the sunk cost fallacy kicks in.  Maybe you’ve won enough success from passion and hard work that you can’t believe this project won’t eventually yield to the same forces.  Energetic entrepreneurs often persevere out of habit or hubris … paired that with a poor business model and, more often than not, massive failure results. Even if the only resources you’re expending are your own hard work and time, sometimes you just need to stop. Here are five telltale signs to look for to know whether it’s time to quit and free yourself and your resources up for something better.

1. You can’t get good data.

The key to completing almost every difficult project is having great information about the issues. Whether it’s numbers or more qualitative strategic insights, without clear knowledge around the problem, you’ll likely make it worse rather than better. Guessing and trial-and-error are fine if you can afford to take the losses when your stabs in the dark miss. But it might be better to stop and take the time to turn on a light. Backup or wait until you have the data and insights you need to attack the project efficiently and effectively.

2. You don’t really get it.

Some projects are just too big to get your head around. If you’re wrestling with something that’s beyond the scope of your knowledge or abilities, it can be tempting to just keep flailing away. But not only will this not move you closer to completion, it can damage your reputation and make you look foolish in the eyes of people whose respect you need. If you find yourself drifting in and out of comprehension when working on the project, take a rest. Complex conceptual work is exhausting. You might just be tired. Come back and try again later. Later, if the core principles still elude you, stop until you’ve found people who have a grasp on the project, and get them to help you. Or transfer responsibility to them and move on. Better to have a slightly bruised ego than a companywide failure on your hands.

3. You can’t sell it.

Not many major projects can be accomplished solo. You need a team of smart people cooperating and moving in synch. If you can’t articulate the core purpose and scope of the project to the people you need to coordinate, you can’t give them clear direction and are likely heading for a big mess somewhere down the road. The moment you sense communication and process breaking down, take a step back. Stop the assembly line before real damage takes place. The stoppage may cause a missed deadline, but a complete breakdown will likely do the same and have far-reaching implications for the project and your career.

4. It’s taking a toll on your health.

It’s amazing how long it takes some people for self-preservation to kick in. Many think it’s a badge of honor to work themselves to physical collapse in the name of duty and ambition. Truthfully, no one likes a martyr. People want to work with others who are in enough control of themselves to be fit, bright and energetic while tackling a project. If you are so involved that you can’t get enough sleep or eat right, you need to stop and reexamine things. If you’re not just sick of the project, but sick because of it, it’s time to stop.

5. It’s negatively impacting key relationships.

If your spouse/partner or children are saying they don’t know who you are anymore, it’s time to stop and reevaluate. If you set proper expectations at the beginning of a big undertaking, those who love you can support you and help you through to the end. But the onus is on you to meet your commitments to those who matter most. On the bright side, if you ignore them completely, at some point you’ll have all the time you need to finish whatever you thought was so important.

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Want more Kevin? Here are three more columns available on Inc.

• 5 Ways You Know it’s Time to Stop What You’re Doing Right Now
• 5 Signs It’s Time for You to Change Careers
• 5 Clear Signs That It’s Time to Fire Someone