I was the recipient of a PIP at my last job, went through the improvement process, and at the end of it, my manager signed off that my performance had returned to acceptable levels. I left about a month later.

So why am I not still there? Well, in the process of going through the PIP and asking myself how I let things get to that point, I realized that I was quite capable of excelling at everything I was supposed to be doing, but I just didn't give a shit anymore. My subconscious had already checked out of that job and was telling me it was time to move on.

When I realized that, my reaction was to start looking for another job while bringing my performance back to a good level. We quit on good terms: they "hired" me back to consult on some problems that came up after I left; I helped someone transition into my old position and I have a job better suited to my personality.