Ask HN: When do you give up?

I run a fairly successful consulting company with under a dozen employees. Have been doing this for two years now and for the past six months it has been replacing the day job salary that I was making before I quit to do this.

Some of the motivations for starting the company:

1) Never had a job that I wasn't bored at.

2) Needed a sense of accomplishment and feeling that I am doing something that mattered.

3) Not being just a COG in the wheel.

4) Wanted to become a better developer and learn the new field (mobile development). Used to be a consultant working in enterprise IT. Never felt I could call myself a real developer.

5) Make lots of Money.

Reason for thinking about quitting

1) Became really good at identifying talent and hiring awesome developers. So now I am relegated to writing proposals and managing client relationships. Original goal of becoming a better developer never materialized.

2) Still have the sense that what I am doing is fairly non-consequential and am under-utilizing the talents of my team working on projects for other startups and companies. Clients love our work, but that still doesn't give a sense of accomplishment. Always feel there is a lot more we could do.

3) Haven't been successful at building our own products. Hard to juggle services and products.

4) Money is OK, but it is linear. More money, only if you get more developers and more projects.

5) Not passionate anymore about what I am doing.

In net, I should just close and do something that I feel a lot more motivated about. However couple of things stop me from doing this.

1) Everyone talks about persistence paying off in the end. I just feel like I might be giving it up easily.

2) Sunk costs. I have already sunk two years of my life into this. All the efforts put into bringing the company to this level will go in the drain, if I give up now.