The lesson of the Samurai

Many are those who will give advice, but few are those who will accept it with gratitude, and even fewer are those who will follow it. After the age of 30, man becomes generally impermeable to guidance. And when guidance no longer reaches him, he rapidly becomes full of pride and self-interest. For the rest of his days, he adds impudence to foolishness, which causes his irreversible fall. This is why it is indispensable to find someone capable of discernment, and to bind yourself to him in order to receive his teachings..

from the Hagakure (spiritual guide for the Samurai, written between 1709 and 1716)