Recently I've been having a lot of conversations about graduate school "rites of passage." I've heard many people echo the sentiment that the purpose of being intensely quizzed by professors during things like journal club presentations (when you present the findings of a recent journal article of interest) or oral exams, is to humble the grad student, to make him or her feel bad about how little they know, and that surviving this is one of the rites of passage that all grad students must go through. As if it were some type of hazing ritual to help thicken your skin. But if that is what you are taking away from this exercise, then you are missing the whole point. Being quizzed to the edge of your knowledge, in front of your peers, is not done to make a grad student feel bad about themselves, or to toughen them up. It is serves two purposes. One, is for faculty to evaluate the breadth and depth of your knowledge, and be able to identify weaknesses that you might have to work on. For example, become better acquainted with the inner workings of a specific experimental method, or to familiarize yourself better with a certain body of scientific literature. In other words, to help guide in which directions you need to grow in. The second purpose is to help you identify holes in your critical thinking abilities and teach you how to question even the most basic assumptions. Why are you using a specific experimental preparation and not another? Why do you use a certain concentration of calcium in your buffers? What is the big question you are addressing? Why does this control experiment matter?
These type of things are good for you, not because they help you develop thick skin, but because they are an opportunity to learn and think about your science in some depth. It is common to join a new lab and start doing experiments the way everyone else does them. And probably this is the optimal way since people before you have been troubleshooting these techniques for years. But that's no excuse for not knowing why and how you do the things you do in lab. One should take all the lab protocols and go line-by-line in order to understand the logic and the reason behind each step.
So my advice to a fledgeling new grad student (any out there who read my blog?), is that, after you complete each of these milestones, before you go off to drink and celebrate surviving being buffeted by professors questions, take fifteen minutes to write down a list of things you were not able to answer, and figure out what your weaknesses were and what you need to work on. Then you can go to the bar and get shitfaced.