1. You don't enjoy it.
This is the most obvious reason to get out of the hole you've dug yourself into. There is no rule that says we are made to suffer. Nothing is more punishing and less rewarding than spending that majority of every day of your life doing something you don't love. The quickest way to free yourself is to just walk away and start fresh, your way.
2. You don't have time for family.
Many of us want to be able to spend more time with our loved ones, but our work keeps us from them. Society has been trained to believe that separation is the natural order of things, but if we just take a moment to think about it we realize that what is natural is caring for your children, being there for your loved ones, helping those we care about and experiencing life with them. Human beings are pack animals, social creatures. Life is meant to be lived with our families and friends, not locked away in a cubicle staring at a computer screen.
3. You feel unfulfilled.
Do you feel that what you do makes a difference or enhances the lives of yourself and others? If not, how can you feel fulfilled? Fulfillment is not to be mistaken with achievement. Making money is fantastic and receiving praise for writing a stellar report is wonderful but unless you are free to challenge yourself, explore your passions and grow in a way that satisfies your innermost desires, you will never feel truly fulfilled.
4. It's not in line with your values.
Morality is a relative term. Many of us are unhappy with our jobs and careers because they quite simply do not fall in line with our personal moral obligations. Personally, I left a promising career in the oil & gas industry because I felt that what I saw was wrong and some of the activities I participated in were questionable. If you feel that what you are doing is having a negative impact on other individuals or the environment, if the culture you find yourself is one that makes you feel bad about your work, it is time to move on.
5. You are underpaid.
Money isn't everything, but I know from experience that the corporate world sees things differently. As an employee, you are meant to provide the highest productivity and value to your employer while operating as a minimal expense. All that means is you are not going to be compensated according to your worth until you go into business for yourself. Even then, the income you generate will be directly proportional to the value you provide to your market. What is fantastic about being your own boss is the freedom to pursue a business doing what you love, and when you love your work, the value you provide will be priceless.
6. You have a bigger purpose.
Each of us has lived a unique life and a unique set of experiences. Each of us has their own perspective and philosophy. Human beings are one race, made differently so that we might know one another and learn from one another. It is our purpose to share our uniqueness to enrich the lives of others, and to be enriched by those we encounter. If your job is not allowing that to happen, then it is not worthy of you.
7. Life seems mundane.
It's a mystery to me that so many of us live life just getting by. Human evolutionary history is one of exploration, wonder, creativity and discovery. Therefore, it is goes against our very exist to be mundane, bored, unchallenged and unfulfilled. If you feel you have a greater purpose in life than working from 9 to 5, sitting in traffic, watching tv and eating junk food it's because you do! We all do! Now get out there and start living your life the way nature intended.
8. You have unrealized dreams.
Travel, wealth, relationships, hobbies, crafts, performing arts. Our list of dreams and goals is as long as it is variable. Maybe you want to be a rock star but you're stuck working as a bank teller, maybe you want to start a family but you can't seem to maintain a partner because your law firm has you working 90 hours a week, or perhaps your passion is traveling the world and writing about the different cultures and traditions you interact with. In any case, if you can't stop thinking about it, you were meant to attain it.
19. Your bosses are narcissistic.
This is a no-brainer. Life is too short to deal with anyone who does not treat us with the level of respect we give them. If you have a superior who is always riding you, makes snide comments, admonishes you in public or private, or is just a nasty personality in general, get out of there now.
10. You dislike your customers/clients.
See above. Again, life is too short to deal with people you dislike. No one says you have to.
11. Stress from work carries over into your personal life.
If work is hard on you to the point that it's affecting your life at home, your relationships, or your health and well-being then that is the last thing you need to be doing. The different aspects of your life are meant to flow seamlessly with each other, not to clash with one another. Work-related stress that carries over into your private life and negatively influences you is a major sign that you are out of flow.
12. Sundays are filled with anxiety and restlessness.
Dreading going back to work. Such anxiety occurs most often on Sunday's but generally does not exclude weekdays. If you feel like Sunday is supposed to be a day of rest and relaxation, but instead it's a reminder of the start to another miserable week. Quit now and abandon those Sunday blues.
13. Getting out of bed is a chore.
If you have to fight to wake up and get out of bed in the morning, you are not living out your purpose. I have had known many people who thought they were just "not a morning person", but began waking up well before their alarm clocks went off when they started working towards their dreams. When you are pursuing personal fulfillment the hard work and trials you face are just as exciting as the rewards.
14. You are capable of doing better.
When you are an employee you are generally limited to responsibility for a single task or a series of related tasks. Feeling dumbed-down and underappreciated is one of the most prevalent causes of depression. It also has a way of depleting people of their charisma, drive and enthusiasm. Don't ever allow anyone to dumb you down. Take a stand and put your life back in your hands.
15. You can't come up with a valid reason not to (paychecks don't count).
Money is no reason to stay miserable. Chances are if you wrote down a list of all of the terrible things that can result from quitting your job, you would terrify yourself. So why don't you go ahead and do that as an exercise. Fold a piece of paper in half down the middle. On one side write down your worst case scenario. On the other side write down how you can mitigate those problems should they actually happen. See! Not so bad after all because there is always a solution. Now, write down on a separate piece of paper all of the possibilities you would find by quitting, your best case scenario, and ask yourself if that is not worth chasing.
If you've answered yes to any of the above, it is a telling sign that you should be looking toward a career change. When my wife and I performed this same evaluation, we discovered a way to go into business for ourselves that anyone can accomplish with some dedication and focus.