I have been part of implementing a PIP on three occasions, two of which at the company I'm at, currently.
In all three of them, our desired outcome was to salvage the employee. Recruiting, training, and retaining employees is an effort that you just don't appreciate until you have to do it.
It's like buying a car in reverse. When you buy a car, you put down a lot of money, and you drive off with a perfect machine. It does everything it's supposed to, and does it reliably. You make your payments as the machine slowly deteriorates, has major repairs, and eventually loses most of its value after seven years. When you hire an employee, you put down a lot of money/effort in recruitment, and have someone who is of limited value to the organization, but as you make your payments, they gain experience. You invest in training, and they develop more capabilities. After seven years (usually less), you have an employee who can perform wonderfully in 4 to 6 key roles, who represents your organization well, and brings value to your team every day.
Now, if you've been there 2 or 3 years, most of the "up-front" costs are paid for. The employee should be very productive in 1 to 3 areas, and be relatively well self-directed. That's where the "payoff" occurs. All the effort you've put into recruiting and training starts to show up in someone you can genuinely count on.
No reasonable employer wants to lose all that investment by just firing you outright. Whatever the problem is, a PIP is there to retain that investment. Sure, a supervisor may not see that, but a manager should, and directors and VP's actually have to account for it.
However, there's a rotten little secret about PIP's: They never address the ROOT issue. They address the symptoms: Attendance, productivity, technical skill, etc. Most of the time the root problem is attitude. RARELY is an inability to learn a skill a problem. Putting the effort into learning skills may be. Mishandling a customer issues isn't the problem. A failure to understand the customer or care about the issue is the problem.
If you're facing a PIP, look at their specific issues. Those are the SYMPTOMS. Now, what is the PROBLEM? Fix the problem, and the symptoms resolve themselves. Treat the symptoms, and the problem will reassert itself later. THAT's why PIP plans rarely work. You can't tell an employee, "Your attitude stinks!" You tell them, "Your customer service satisfaction rate is low." The reasons are many and varied. A "Bad attitude" claim is subjective, and difficult to defend in a wrongful termination suit. A "Customer Satisfaction Percentage" score is objective and easy to prove.
So, if you want to survive the PIP, you have to figure out what your PROBLEM is, and fix that.
Not to lay it all on you, though. You can't make an elephant fly. If you're in the wrong job or career, you need to face that possibility, too.