Many junior scientists need to take a hard look at their job prospects
The longer students stay in a PhD program, the less likely they want to be professors. Typically many first year students say this, but the numbers quickly drop off in later years.When I was a PhD student, I gave a few talks and blogged about this issue. I would present all these statistics in my talks about what they needed to do to be competitive, and people just absolutely hated me for it. One person said she wanted to punch me in the face. That said, she emailed me years later to tell me that she became a professor, despite those statistics. If you have a lot of tenacity (doing a postdoc), are willing to settle for a school that isn't top-50, and are reasonably productive (a few papers per year) it is doable. Every single one of my friends that graduated and still wanted to be a professor, is one now, but it took 3-5 years of additional work.  This is true for my friends in psychology, computer science, EE, and neuroscience.Of course, now all my other friends say, "Why the hell did you choose to be a professor where you work 80 hours per week and make less than most undergraduates with CS degrees, even when your area of expertise is AI?"Lastly, I want to add that a PhD is a degree in learning how to do research and in becoming one of the world's foremost experts on a particular topic. There are lots of great things to do with a PhD that aren't being a professor.