I've happily noticed recently that some friends from grad school and other people I've met around the way are about to begin their first jobs. This got me to recall my first job, particularly the difficulty of transitioning to it. My first year I felt like a fish out of water. Although I'd finished the dissertation and taught summer classes in grad school, I found having to teach my own classes of a few hundred students apiece while simultaneously writing publishable articles to be spectacularly daunting. I spent almost the whole year working on papers that went nowhere, and my teaching wasn't that great (writing papers *and* teaching multiple courses for the first time is tough work!). Like many people in these circumstances (or so I hear), I contracted a serious case of Impostor Syndrome: the deep conviction that I was completely incompetent and unfit for my job.
Ultimately, like most afflictions,the syndrome eventually passed. Although it still raises its ugly head from time to time (in response to brutal paper rejections, etc.), in my case I found that the way through it is to simply keep working, seek out feedback from others (even if it's uncomfortable), and wait it out.
Here, then, are some words of encouragement to all the new faculty and post-docs out there. You are not an impostor. If you made it through grad school and got a job, you have what it takes. You have accomplished a great deal and leapt many hurdles. Your first year will most likely be very hard. There will likely be many times that you feel completely lost and inept. Try to be good to yourself. It is your first year, after all. You'll figure things out in due time. Just be sure to put yourself out there and ask for help and advice from others. Yes, not everyone will be so helpful, but some people will, and their help can make all the difference in the world.