If it is worth doing, you’ll want to quit

“Should I quit or hang in there?” is a question that will accompany any worthwhile project. If you’re not tested, the work probably isn’t on path towards the success you’re hoping for.

“Never quit something with great long-term potential just because you can’t deal with the stress of the moment.” –Seth Godin, The Dip

You will feel tested. You will be challenged. You will want to quit.
Decide the circumstances that are acceptable to quit and hold yourself to those guidelines. When work becomes hard, great rewards are usually on the other side. Don’t be afraid to sacrifice short-term comfort for long-term gain.