forever chemicals had one job
The problem is that the structure of the PFAS (a fluorocarbon chain with an OH at the end) looks a LOT like a hydrocarbon chain with an OH on the end... that's a saturated fatty acid which is crucial for body metabolism.
Compare the structure of https://en.wikipedia.org/wiki/Myristic_acid and https://en.wikipedia.org/wiki/Per-_and_polyfluoroalkyl_subst...
This allows the body to accidentally substitute a PFAS (which does nothing) for a fatty acid (which does something - and often important things).
https://www.vox.com/2022/8/25/23318667/pfas-forever-chemical...
So yes, it had one job - and it did that job well. It also looks like something that has another job... and does that job really poorly when substituted.