Performance improvement plans are how we fire people. You don't end up on one unless someone wants you out. It's all about making a paper trail to avoid lawsuits. If they are really determined to get rid of you, no amount of effort or skill can save your job. It is too easy to make these things look reasonable on paper but completely unattainable in practice.
In over 10 years here I have never heard of someone's job being saved once a PIP starts. Not saying it doesn't happen, just that I haven't seen it yet.
Unfortunately, @OmOBw3A-1rva is right, I am yet to see performance improvement plan result in something else but being cut. And it was never truly about the person's work performance - they need cuts, this is how they get them consequence free.