Sometimes there are honestly mismatched expectations or understanding of how performance is measured and evaluated. Other times, people assume new roles, and some aspects of the new role are not prioritized correctly or just not working out. I have witnessed some such cases, and personally managed one.

Working like hell does not help if the effort is expended in the wrong place. That's where the first 1:1 will be a clear indicator if the correction is working or not - if it's not working it may be a failure of a honest PIP, or PIP dressing up a decision that has already been made. But honest PIPs exist, and sometimes they do work to solve a problem that was not being solved by itself.