There are many non-academic training programs that are extremely tough, like military education. These usually require a certain level of fitness assessment to be passed during recruitment. The recruits also know the kind of exigent demands that they will face. After that, the demonstration of the required physical and mental fitness is again assessed during resocialization and initial training.
Usually, academic courses require only an assessment of basic medical fitness. The students do not look forward to any inordinate levels of endurance challenges during their academic pursuits. Often the students who have been accepted into academically challenging and competitive courses like Medicine are highly intelligent, hardworking and passionate. Yet most of them are not ready for the arduous intellectual and endurance boot camp training medical education actually is, leading to a very high level of mental disorders in medical students, caused due to the demands of the course itself. This Time article is an enlightening insight on the issue. Also seen is a high level of cardiovascular diseases after one has been in the medical field, doing residencies in demanding specialties and stressful jobs with poor work-life balance.
Similarly, among the different academic courses one could do after schooling, some are especially grueling. Although the Bachelor's and the Master's courses in sciences have about the same level of difficulty across similarly ranked universities, the PhD courses are a different kind of experience to many. In this Nature article, "PhDs: the tortuous truth", the results of a survey of more than 6,000 graduate students reveal the tumultuous nature of doctoral research. If you are looking to understand why a PhD can be challenging, this brief article and this article will be helpful.
The common themes that run through these articles are loneliness/isolation, long hours of work, stress, feeling unsupported (by peers, supervisors, institutions), insecurity arising from the unknown (the outcomes of your research, future career), the need for self-motivation, lack of economic incentives compared to similarly talented peers in other jobs. and the nature of the work which does not offer frequent rewards, positive outcomes or encouraging boosts. One just has to go through the posts of PhD students in forums and on Twitter to get an idea about the mental turmoil many face, and how hard it is for students with physical challenges or family responsibilities.
It does not help that the traditionalists, in both medical education and in research education, think that supporting may be mollycoddling and the best a teacher can do is to toughen you up, prepare you for the world, and help you to learn all by yourself, the hard way. Just the way they did it. In both these cultures, one can often find behavior from superiors that enables the imposition of a severe physical and emotional toll on students.
The nature of the course already threatens to break the vulnerable students, and it is in the hands of the teachers whether they steer the directions gently, facilitate the learning and guide the student during challenges to bring out the best in a student, or they subscribe to the idea of letting the student do it all on their own, for "their own good". It is not uncommon to have work cultures in both the courses (link, link) where the student feels belittled, humiliated, harassed.
What then is the answer to the question, "Should I do a PhD?"? I think the first point to consider in replying this is a question, "Why do you want to do a PhD?". Once you have the why, you can endure the how ("If we have our own why of life, we shall get along with almost any how." - Friedrich Nietzsche)*.
If advancement in your current job demands it, then you should never lose sight of that future goal or long term reward to sustain you through the dark times. Some might stumble into a PhD unsure what to do next after a Master's, or buying themselves more time before they quit the student life, or pressured into it by someone else even though they themselves do not particularly want to do it. It is easy to see that these people may be especially vulnerable to feeling trapped, stressed, depressed and disillusioned, unless they are resilient by nature, or develop a passion for the course, or are fortunate enough to land a really fortuitous, smooth-sailing experience.
Others, who have been bitten by the research bug, are the kind of people who cannot think of anything else they would rather be doing. Often they are used to prolonged studies in isolation, so they may not struggle as much with the long hours spent alone. But they can still feel lonely because there are so few in the society who understand their experience. A good friends' circle or support system is essential to de-stress. While the motivation aspect may not be a problem in these students, still they can face the other challenges like delay in developing a clear vision of the path/strategy; ideas and approaches not yielding the expected outcomes; pressure of publications or difficulty in publishing; conflicts with supervisor; financial/social/family stresses and so on.
So there is no "one size fits all" answer to the right or wrong of doing a PhD. You should have curiosity, creative and innovative thinking, ability to come up with multiple ways to approach questions, and optimism as core personality traits or skills, before you want to try for a PhD. You should be ready for long work hours, social isolation, a LOT of reading and an unspecified length and trajectory of the course if you embark on a PhD. Once you are doing a PhD, you should try to learn time management, develop interpersonal skills, take up self-development and self-care regimens and work towards developing psychological resilience. Keep the broader picture in mind to keep yourself motivated. Make friends. Find mentors. Mentor new students in your lab. Have fun working and celebrate small victories.
It is important not to lose the wondrous love you have for the subject and to nurture the bug in your head that keeps you awake at night, making you impatient to go to the lab and try out or read up on this new idea that has struck you. And remember, once you take care of these aspects, then you can control the narrative in your mind to make your PhD one of the most memorable experiences of your life. Probably you will never want to go through it again, but you will be glad that you did it and will think of it as one of the amazing times of your life.
*1976 (1954 and 1968 Copyright), The Portable Nietzsche by Friedrich Nietzsche, Translation by Walter Kaufmann (Princeton University), Section: Twilight of the Idols or, How One Philosophizes with a Hammer, Chapter: Maxims and Arrows, Quote Page 468, The Viking Press, New York.