Quitting your business doesn't mean you have necessarily failed. It could just mean it is no longer a right fit. There is nothing wrong with quitting when it is the right reason and decision for you. Now, the question is when do you quit and when do you push on and hope what you are feeling is just a "phase."
WHEN YOU DON'T LOVE YOUR BUSINESS
This should be the easiest red flag for you. When you start your business, it is all you can think and talk about. You are working your butt off and into wee hours because you love what you are doing and time just passes without you realizing it is 3am on a weekday. You literally put all your time and energy into the business because it is what you want to do and you have zero regrets doing this. When you stop doing all of this, you know you don't love your business anymore.
WHEN YOU ARE NOT MAKING MONEY
Yes, some businesses are not meant to make money and they have other goals or purposes. However, if you started your business to make money and you are not. That is a red flag you cannot overlook. Financial stability of a business is a major factor. If you are not making money initially, that is fine, you will get there. If you have been going at this for a while and not only are you not making money, you are losing money every month, re-evaluate FAST. Decide if you need to make changes to your business or if this just isn't going to work out in the long run.
WHEN OTHER PRIORITIES START TO TAKE OVER
Or when you start prioritizing things differently. You value things differently now. You might now value some down time or value sleep over networking and connecting with more people on social media. You might want to start eating well, at the kitchen table, with no devices. You might want to slow down and not have to juggle 50 things in the air. Reality is, you want to do other things that is not related to the business.
WHEN YOUR BUSINESS DOESN'T FIT WITH YOUR LIFESTYLE ANYMORE
We all change and our lives evolve. Despite your best intentions to run a business, some factors interrupt it and there just isn't a great way around it. These factors might be finding your significant other, having kids, having aging parents move in with you. External factors (no matter how personal they are) are another reason to really think about the future of your business.
WHEN THERE ISN'T ANOTHER SOLUTION
If you checked off all of the boxes above and you cannot find a solution to rekindle your love for your business/ start to make money/ move distractions and road blocks away, you know it maybe time to move on. Hard decision and hard questions to ask yourself but the reality check is needed sometimes.