"A man who hardens his neck after much reproof will suddenly be broken beyond remedy"
hardens: This is something that the person does; their self-will rises up and stiffens them against counsel – both friendly and divine.
There is a point in which God will just say “ENOUGH” and will severely limit a person's potential, ability, opportunities, etc. Realistically they did it to themselves, but they will be broken and unfixable. Grace will come and work its wonderful work, but one cannot go back when the hardening is of such a nature that a breaking had to come.
There will be no remedy. This is so strong, but it is truth. There are some consequences that are unrepentable. Things will stay broken. We are a society of second and third and fourth chances, but at some point they run out. Even the God of lovingkindness and mercy and grace at some point pours out His wrath. At some point in the righteous ruminations of His mind, He is able to say “no more” and the person pays a heavy price for their refusal to submit to the gentle tug of God.