There are always reasons either to stay or to quit a company. Although quite often employees need to find strong reasons to stay, in some cases quitting can be the best solution. Look thorough the list of situations that make any job unbearable and not worth staying at. Consider if you really need this job or it's time to start a new life.
Your company is undergoing crisis times. Promotions are not granted, new people are not hired, and layoffs are highly possible.
You've failed to establish friendly relationships with your supervisor, or you have once destroyed them and there is no way back.
You may have started as an unexperienced beginner who could stay late hours and be satisfied with a comparatively small salary. After some years in the company, you have changed your life status to a working parent, who needs more financial benefits and can not afford overworking.
Corporate policy contradicts with your own views. It's hard for you to establish a positive attitude to the company.
You simply fell out of love with this job. You'd like to do something else. This situation is similar to falling out of love with a person – when everything is said and done, the only thing you can do is to split from each other.
The company is doing something unethical, for example, managers do not tell the truth to customers, or the company service is not efficient at all, although it costs a lot, or the company is trying to violate existing laws. No matter what exactly is being done unfairly, you'd better not take part in it.
Due to some reasons you have established the reputation of a bad employee (you've been constantly late, did not perform greatly, failed to fulfill your duties, etc). This job might be just a wrong job for you.
The work environment is unhealthy. Team work is impossible because people do not get on well with each other. You do not feel comfortable at work, and you are constantly in low spirits.
You are constantly stressed, and this affects your emotional and physical health, along with your personal life. You do not enjoy your free time, can not party with friends and have problems with falling asleep.
You have overgrown this position. You need more responsibilities and more challenging tasks. This company simply can not provide a professional like you with further career growth opportunities.