>>azhenl+(OP)
Berkson's, right? A perfect interview process would result in a population where none of the people who are hired as a result of it have any attributes that could be correlated with job performance. i.e. all the information has been 'used up' by the selection filter. If you have a correlation, then you can improve the selection filter, so it can't be perfect.
This can have interesting outcomes. For instance, when Triplebyte published their blog post about which environments get the most hires⁰, it revealed the areas they haven't yet entirely accounted for in their quest to increase matching performance.
0: https://triplebyte.com/blog/technical-interview-performance-...