- You suffer from depression (inability to concentrate, insomnia, feeling sad all the time, having no energy when you wake up in the morning, constant feeling of fear and anxiety, etc) for more than a few month
- You did thorough research on the amount of time, money, and energy it will take to get a PhD and you think that, given the employment prospects, it's simply not worth it
- You don't think you want to be a professor. Again, every researcher, no matter how successful he or she is, has some periods when he or she feels like quitting. However, if your attitude towards the profession doesn't change for more than a few months, then you should consider quitting.
- You feel your work has an irreversible negative impact on your health. Trust me, losing your health to be a professor is not worth it. This career is not that lucrative and important to justify the sacrifice.
When deciding on whether to quit your PhD program, here are a few things I think you need to avoid:
- Don't listen to your friends and family. Don't continue your PhD program simply because you feel obligated to them to get the degree. Despite having your best interest in mind, these people often have no clue what academia is really like. They are as naive as you were when you started your PhD program. They think that a PhD is a ticket to wealth and status, BUT IT'S NOT! I often meet quite intelligent people from outside of academia who think that a person with a PhD can land any high paying job he or she wants.
- Don't be stubborn. I think most people who come into a PhD program are of the type who don't give up easily. They are used to finish everything they started despite all kinds of hardship. The thing is that you stubbornness may lead you to the same state of despair years and thousands dollars later. I would applaud a person who year after year keeps trying to become a millionaire, discover a drug against AIDS, or pursues some other big dream. But I would think that a person who is doing the same thing to get a hard, low-paying job of an English teacher is simply crazy.