He asked me for my honest opinion on whether I was performing at the level I could (I thought I could do better), and what things I thought were causing it. I named things about me, things about the team, and things about the company in general. He explained the PIP was a deal: for three months he would take care of the external factors, and I would take care of the personal ones. We came up with a project for that quarter, which would be the metric with which I'd be evaluated.
If nothing had been done (no PIP, no anything), I might have been fired during that year. But we all wanted me to perform better; me, my boss, and the company that designed the process. And so all sides were willing to change reasonable things to make it so. Because of that honest conversation, and that feeling of all of us being on the same side, I recovered and have been going strongly for years.