You dream of walking into the boss's office and saying, "Woot! I won the lottery. You can take this job and...." But in reality the odds of winning the lottery are way too low to ever go through with the threat. So, now you need a back up plan, because giving notice and having to work through two weeks of hell is beyond what you're willing to bear.
Health and Welfare
If you doctor has advised you that your job is detrimental to your mental or physical health, your employer will likely understand when you do not give notice that you are quitting. He will also understand if you need to quit to take care of a critical ill family member, especially if the illness or injury was sudden and the need for care is urgent now. However, before you give notice, see if your employer offers a long-term medical leave program. You may be able to take time off to heal or help you family without risking your job.
No job is worth risking a police record. If you are ask to do something illegal by your employer, you have every right to walk off the job and report the violation to the proper authorities. Your employer is not likely to pay your bills while you are sharing a cell with an axe murderer. Besides, no one looks good in prison orange. You also are not expected to stay at any job where you are the victim of illegal activities, such as harassment or assault.
Ethics and Morality
If you employer asks you to do something that goes against your ethics or sense of morals, ask yourself if you paycheck is worth the the guilt and sense of lower self-esteem you may suffer. If the answer is no, then you are within your rights to quit before you do anything you will regret. Before you walk off the job, though, consider discussing your concerns with your employer. If he understands your ethical dilemma, he may find reassign the project to someone else.
Whenever possible, you should give at least two weeks notice to allow your employer the opportunity to redistribute your workload or to hire a replacement. By giving notice, you maintain a good relationship with your employer. If you fail to give notice your employer may report to future potential employers that you quit without notice and you are not eligible for rehire. Potential future employers will be concerned that you will also leave them in a lurch. On the bright side, you might get lucky. You may give notice and be promptly shown to the door—and freedom!