Here are some of reasons possible for which you should not pursue a PhD:

1. If you are after money. A PhD will not guarantee it! You can work in industry and will not need a PhD for that and earn more experience while making decent money and connections and start your life earlier. You need more than a very minimal amount of money to live on. Getting a PhD takes you out of the workforce for 4+ years, during which time you make very little. Anyone with the ability to earn a PhD likely has the ability to make a lot more money elsewhere.
2. If you are incapable of enduring for the rest of your life to work much harder than your fellows.
3. If you are having no good communication skills. You need to be well coordinated to be successful, unless you’re a genius…
4. If you don’t have a strong interest in the topic. Getting a PhD takes quite a while, and is financially stressful. If you’re not highly motivated, you’re unlikely to finish, and then you’ve lost a lot of time and money without even having the degree to show for it.
5. If you’re not willing to spend a lot of time reading and rereading. Getting a PhD requires making a significant contribution to the literature, which means knowing what’s already in the literature, which means reading many papers.
6. If you are antisocial. Just like in any other career, you will not go far in your research career without a decent social skill.
7. If you are arrogant. You believe you are intellectually superior to everyone, and so don’t listen to advice from your advisor and colleagues.
8. If you lack of self-confidence. A PhD requires that at least at some points, you need to believe you have good ideas, and to push those ideas forward (during meetings with your advisor, etc.). It is still possible to do a PhD simply doing what your advisor tells you to do, but it wouldn’t count as the best use of your time (you won’t learn much).
9. If you lack of communication skills. Minimally, you need to communicate with your advisor. You can get a PhD by simply following orders, but a lot of interesting problems come about because a student tells an advisor, “I did that experiment last night, here’s a little thing I couldn’t explain. “
10. If you are lacking adaptability. You will try a number of projects in your PhD that will fail. If it becomes clear a project is not going anywhere, you need to drop it and move on to the next thing, instead of sinking more time into a dead-end.