When is enough enough?

When you have done your best and can do no more without personal injury, breeching the bounds of ethics, harming others, or resorting to illegal activities.

When it is clear that a hope, a dream, an expectation, or a vision is not going to happen.

When some plan is not working now, and will not work in the future, without doing harm to others, lying, cheating, or fiddling the figures.
When the cost of some enterprise, in terms of hours worked, people harmed, relationships ruined, or principles and values compromised, exceeds any possible benefit in anything but monetary terms.

When continuing in the same direction will destroy any civilized standards of workplace action.

When the only outcome is more money, more status, more power, or more responsibility—and you cannot spend the money, wield the power, handle the status and responsibility, or live your life, without destroying who you are and the values you want to live by.

From Slow Leadership