As a (perhaps permanent) refugee from academia, my $0.02.
You get out of academia what you put into it. If you go in with no plan of action or just wanting to be like your mentor/advisor, or solely dependent on his funding or the department's TAship still thinking this is like undergrad, but only you get paid for it, you will be in for a rude awakening.
The signs do take longer, maybe one or two years, but they are there. Your prospective advisor has no pull in the department, or can't twist elbows and get a RAship for you. Or he puts you on a project to reproduce someone else's experiment with unreplicable results. You start to notice his papers with foreign colleagues have serious mistakes that get through peer review. You wonder why he hasn't been properly funded in years.
I managed to get out alive, with a degree and a good publication on the way (with people at another institution), despite one adviser leaving the university nine months after I joined and everyone else being broke. How did I do this? I came in with a overarching research goal (learn how new techniques in quantum information could be used to solve chemical problems), one that encompassed more just my advisor's research area. I executed on the overall goal and when things got harder, I doubled down even more. I didn't let departmental barriers stop me from learning what I knew I needed (quantum field theory for condensed matter) to solve problems, even if those courses weren't in my department and even if the connection wasn't immediately apparent. I sought out conferences on my own, paid for them myself, networked my way into summer visiting positions and invited talks, because nobody was sitting there and spoon-feeding me little bite sized research topics. In fact, I lived in my office for three months when I couldn't afford rent anymore and no one gave a shit. I am reasonably sure people would probably have taken 3-4 months to wonder where I had gone to had I jumped off a bridge.
My central point here is that many people in grad school don't recognize that your adviser's interests and incentives are not necessarily your own (just like your boss's). Unlike your boss, your adviser will never be held responsible for bad management. If your _department's_ incentives and interests become unmoored from your own -- well, then in the words of Mr. Garrison it's a "big lowercase t for time to leave"
The sooner you recognize that and find a happy medium between your needs and theirs, the sooner you can be productive for all concerned. Every contingency measure I took in terms of classes, planning, networking in terms of the overall goal, all were leveraged and all were necessary to bring things to a reasonable close.
I know this was posted here a while back, but this really is the best description I've read (he finished, while I left with a Master's and may go back elsewhere but the hustle necessary was much the same.) http://www.pgbovine.net/PhD-memoir.htm