As a postdoc at the time, I couldn't yet say whether being a faculty member could be anything like being a postdoc or not, but equating a tenure-track faculty position with a postdoc didn't sit right with me. (It was also, in my opinion, easier to write about not caring about tenure *after* having gotten tenure.)
So, let me be on the record, writing publicly and openly about my thoughts about the tenure-track, in the thick of it. I've been an assistant professor for three years now, halfway through. I can say unequivocally, that my job is not like being a postdoc, nor should it be (with the side-note that certainly postdocs and graduate students have some of these responsibilities as well, but I'd argue to a different degree).
1. I am responsible to so many people.
I am a researcher, a supervisor, a mentor, a teacher, a writer, a role model, a boss, a collaborator, a PI, a grant writer, a grant manager (hopefully), a mediator, an editor, and an advocate. I manage people and projects. I need to think of projects that I think will be successful to work on together with the people in my lab, and contingency plans if those projects fail. I need to find ways to compensate these people. This includes startup (which ends at the end of this month - we get three years here), and writing applications for funding to so many different agencies (government, foundation, internal, inter-institution, you name it, I'll apply). I never appreciated how terrible it would feel to tell someone I can't afford to pay them to continue doing the great work they are doing.
2. I am a gatekeeper.
I am in a position of authority over others in a way that I wasn't as a postdoctoral fellow or a graduate student. I can affect the trajectory of trainees in so many ways: grades, admissions, recommendations, candidacy exams, thesis defenses, access to collaborations and professional opportunities. I have the power to intentionally harm an application by giving a bad recommendation. (Note that I won't agree to write anything but positive recommendations.)
More insidiously, I learned in my first year as a professor that I can unintentionally harm an application - not just in gendered language, I was aware of that - but in all the content that people expect in a letter of recommendation for different types of applications. I hadn't sat on these committees (I have sat on several now), to see how skillfully some professors deploy the letter of recommendation to really make a strong case for the applicant. Whoa. Happy to talk about this more later.
3. It can be lonely.
The cohorts typically keep getting smaller, from the number of other people who are undergraduates that you can interact with, to the number of graduate students that you interact with, to a dwindling number of postdocs, to you, as a new professor. Depending on the size of your department or institution, there may be a a few other new professors, but likely not that many. That isn't to say that there aren't more established professors for one to interact with, but the interactions, in my experience, have been fewer and further between. I don't know what I was expecting, but I wasn't expecting the number of daily interactions to be this different (reduced) from being a postdoc.
4. There are new expectations for interacting with the lab.
Merging the three previous thoughts... one inclination I had/have is to treat members of my lab as peers. But, it's more complicated than that because of the power dynamics. The members of my lab are definitely colleagues. Per Wikipedia:
"Colleagues are those explicitly united in a common purpose and respecting each other's abilities to work toward that purpose."
While a peer is someone:
"that is of equal standing with another"
I have the ability to shape letters of recommendation, open doors, close them, or otherwise influence the career trajectory of people who are in my lab. By virtue of that, I need to be especially careful to recognize that we are not on a level playing field. There is a power imbalance. The people in my lab are not complete free to speak their minds with no fear of potential retaliation. They can't decline my invitations without a twinge of concern that I might interpret it negatively, even subconsciously. Given how academic institutions and funding structures work, there are so many concerns for them, literally for their livelihoods.
Sure, as a postdoc, I could, some day, have an effect on my peers, and on the graduate and undergraduate students in the lab. But I wasn't directly above them in the food-chain. If they didn't want to come hang out, it's no biggie. More than anything, this transition has been the one that caught me off guard the most.
Can I hang out with my lab? Of course.
Do I have to be constantly aware of how there is a power differential that is tipped in my favor? Absolutely.
Not a postdoc, but still a person.
I have responsibilities to the students in my class, to the members of my lab, to my peers, my colleagues, my administration, and to the public. I feel the weight of this responsibility. As a professor, there are so many more ways for me to fail. There are so many more people for me to fail. Being a professor on the tenure track is not like being a postdoc in many ways. But, maybe in the ones that matter most, it is: this is my life. I'm living it right now. It isn't on hold.