Absolutely not. A performance improvement plan will generally not be successful if HR and the manager are not fully supportive of the employee and their capability to improve. In those cases where one or both do not truly believe the employee can improve, then odds are that this belief will become a “self-fulfilling prophecy” and the employee will fail to achieve the desired improvement.
What will ideally happen is that the employee will face the facts presented about their performance and latch on to the clear definitions of success and tools to help them get there. The employee will “lean in” and do anything in their power to raise their performance level fast.