In short, "you can't set the settor." It's a bit like saying "everything is subjective". By asserting such, you're proclaiming subjectivity as objective, breaking the whole statement.

For anyone who'd like a deeper dive into the logic behind this, Bertrand Russell's Barber Paradox[1] is a fun one (not to be confused with Lewis Carroll's "Barbershop Paradox.")

[1]: https://en.wikipedia.org/wiki/Barber_paradox