To add to the great answers here already, I'd also say that a sign for me to quit something is when it no longer serves the intended purpose I initially sought it out for. I think many people get caught up in the "sunk cost fallacy" of continuing on with something just because they've invested so much time, effort, resources, etc., and also maybe because of the work it takes to let it go, but they don't necessarily take stock into whether it is truly meeting the need you had from the very beginning. Granted, needs change and circumstances do too, so therefore if you no longer have that need and/or this venture is providing some other value to your life, then it can make sense to stick to it or keep it around. But, if you don't enjoy it anymore and it's negatively affecting you and/or others around you - as the others have said - AND it no longer is doing what it was supposed to even be doing, time to send it out to pasture.