When I was an undergrad, I did research. I worked in a lab for 1.5 years (full time over the summer), participated in group meetings, did my share of lab maintenance, and worked with grad students. I thought I knew what grad school would be like. I was completely wrong--grad school threw me for a total loop. I felt lost (there was no clear path to get to my degree). I had all this time, but yet no time at all. Progress was really, really slow, and I was so clueless. I had no idea how to manage my time effectively without classes and deadlines to help me. I didn't know how to properly test things or document them, so I had to repeat a whole series of experiments. I didn't know about all the time TAing takes, all the different pressures on students to study and finish experiments and do this side project quickly and train this new student and help this undergrad in lab while still making progress on my own stuff.
When I was a grad student, I worked with postdocs. I thought I knew what being a postdoc would be like. I was wrong. As a postdoc, I was now THE expert on my technique. My National Lab colleagues were relying on me, ME! to tell them if certain experiments were possible, if certain data was reasonable, if certain timelines were realistic. I had no backup. There was no one else on the project who knew my technique (which is what I was brought in for), but I knew nothing of the system I was studying (which is what I went to learn). I panicked quite a bit when I realized that, then knuckled down and did it. Being a postdoc (at least in my case) was a lot more responsibility and a lot more independence than being a student. It took a lot of getting used to be considered an expert after all those years as a student.
When I was a student, we used to sit in the lab and wonder what our advisor did all day. We would laugh about it actually. Now, I am drowning in it.