If you've been out of the job market for a long while--or for even a little, there will definitely be days when that sense of desperation will creep in. You'll grow weary of cutting back on everything and counting pennies and are willing to accept any job you can find.
Then along comes a job interview for a position that, when you interview for it, you discover is a little out of your reach.
And you know it.
But you want that paycheck, so you tell yourself "I'll figure it out, all of my old bosses have LOVED me! How hard could it be? I'll be totally fine."
So you take the job.
Maybe you've never been let go because of performance issues (and the saying holds true that everyone should be fired at some point in their career. It's a real learning experience, and you NEVER make those mistakes again.). You don't know about that troubled feeling in the pit of your stomach that keeps you hungry to KEEP a job once you've got it.
You can't believe that you could get fired. So you don't take extraordinary measures to make sure you keep the job that was a little out of your reach in the first place.
And you get fired. And you didn't have to be.
I'm not saying that you shouldn't take a job that stretches your abilities, but once you're in that job, you've GOT to work your tail off to keep it. Just because every other boss has loved you doesn't mean that this one will. Just because you've always received stellar performance reviews doesn't mean that you couldn't stumble into the one job on the planet that isn't a totally natural fit for your abilities.
Every new job is a new relationship. Your old jobs got you the new one, but the similarities stop there. It's a new playing field with new players and the only way to stay in the game is to keep bringin' your A game.