"Should I quit?" is probably one of the most popular questions on this forum.
Here's the easy way to know whether or not you should give up on your project.
Answer these two questions:
Are other company's making money selling the product that you have built/are building?
Do you accept the fact (and are willing to adhere to it) that to be a successful entrepreneur, your life will be 99% marketing and 1% building?
If your answer to either one or both of these questions is no then you should give up.
This is because if:
a) nobody else is making money from your product then your going to really have a hard time marketing it
b) if you're not willing to put the work in to market your product, then you're never going to succeed as an entrepreneur.
However, if your answer to BOTH of these questions is "yes", then stick with it.
Other businesses are making money with your product, therefore there is no reason you can't too. All you have to do is market it correctly - and if you're willing to put the work in, you can succeed.
Scared? Worried? Don't like failing?
These aren't real reasons to give up. You're going to feel them regardless of how well your business is doing. You'll be scared of failure even when your business is successful. That's just the human condition.
I think that 99% marketing depends on your project. Some projects are more tech/product focused and some are more marketing focused. It also helps if you have more than 1 founder so you can delegate all marketing to your co-founder ;)
Aha :-)
However, for me, focusing primarily on the tech/product is the main reason the vast majority of startups fail.