Graduate school can be a very trying time, emotionally and physically. There are often extended bouts of work with long hours as well as bouts of loneliness and trying to understand ones motivations. The emotional stress can be the most difficult to push through. It is essential for every graduate student to understand exactly why he or she is doing what they are doing, as well as to understand how what they are doing will ultimately lead to enhanced life quality.
In addition to whatever the graduate student researches, he or she must study evolutionary psychology and philosophy. These topics are very important to having a truth based understanding of the world, and ultimately lead to a more fulfilling existence. Anyone who bases their morality, philosophy, or thoughts on concepts like religion and mysticism will likely end up having some sort of psychological damage. Religion is full of contradictions, and trying to cope with these and their impact on your life while trying to be a productive graduate student will be very difficult. If you are religious, try this prescription for freeing yourself from religion (credit goes to cspice):
Have a conversation with "god". Tell him that you have never seen proof or felt any aspect of his existence (as no one ever has; there are always scientific applications for the feelings that people get when they pray, or near death experiences, etc). Additionally, since he "made" you as the logical, rational person you are, he knows that you could never believe in anything without objective proof. Therefore, it is actually impossible for you to believe in anything supernatural, i.e. god, Jesus as the son of God, etc. So, tell god that unless he gives you objective proof of his existence in the next month, you will stop going to church and being religious in any way, and, additionally, god cannot punish you for this because you are just acting in your nature.
Hopefully, you are on your way to being free from religion now. It is important, and indeed, right, to be a logical, rational person. But anyway, why should we study these things?
I would recommend starting by studying evolution. Science is important for the logical thinking person to study in general, but studying evolution has a special purpose. It helps us to understand people. No matter what anyone will say, no one in this world is completely autonomous. We must deal with people. My recommendation to start on evolution would be to read Richard Dawkin's "The Selfish Gene". While this book can sometimes be somewhat tedious and boring, it is very useful for providing a working model of evolution to the average person. The basic idea of the book is that a gene which is ruthlessly selfish will propagate. This is almost self-evident, but the implications can be very interesting. Understanding evolution will help you to understand yourself and why you feel certain ways. Additionally, it will give you a working model for understanding the actions of other people. This leads to studying psychology. Psychology, in its proper form, is the practical application of evolution to the human species, in addition to cultural, non-evolutionary effects. As a graduate student who interacts with a lot of people, you will face many who are irrational and chaotic. You may, at times, blame their behavior on yourself, and sometimes it is your fault, but if you know anything about psychology, particularly evolutionary psychology, you might understand their actions a little better. By studying evolution and psychology, you are going to have a leg up on the average person in understanding your own motivations and actions as well as those of others. My book recommendation here is "The Red Queen: Sex and the Evolution of Human Nature" by Matt Ridley. It is actually not really necessary to study empircal models for psychology or any non-evolutionary approach as this does not lead to greatly enhanced understanding, and is much less unified and objective than the evolutionary approach.
Finally, we need to tie all of this together into forming your own personal philosophy. It is important to be exposed to the concepts of objectivism. I would recommend, above all other books, to read Ayn Rand's "Atlas Shrugged". This book has changed my life and helped me to understand my motivations more than anything else. The way I describe the philosophy is that it is a prescription "to love your own life". There are many resources online to read about objectivism, but I recommend reading the book above all else. As an example, I used to be someone who was afraid to "take up space in the world." I saw myself as someone who was weak, and felt grateful if anyone spent time with me. As a graduate student, we are particularly prone to this feeling because we are in a totally different situation than so many of the other people in the world. However, after understanding the value of my own life, I no longer feel this in any way. My confidence has increased 10-fold, and I now have strong convictions and goals rather than just floating through my life and taking what table scraps I can find. If I see anyone who is depressed or lonely, I recommend for them to read "Atlas Shrugged".
I cannot fully explain why it is so important to study these things, but hopefully I have convinced you that these three books are worthwhile. We face a lot of challenges as graduate students but questioning ourselves and subjecting ourselves to the whims of others should not be one of them. By studying evolutionary psychology and philosophy, the graduate student will have a better understanding of the world, feel more motivated than ever, and have a more fulfilling lifestyle.