In a word, death.

True wisdom is based upon death. It doesn’t come from experience, people who say it comes from experience are still like little children who want to know everything and control everything. Wisdom is not knowledge, wisdom is surrender. Speak to a terminally ill teenager who has accepted he only has 6 months to live and you’ll see what wisdom looks like. You’ll need to be pretty blind not to see that he’s wiser than almost everybody else. Might even send chills down your spine. He will surely not be able to relate to your problems.

The closer you are to death, the wiser you are. Surrender to it completely and you will jump into it with your body still alive. That’s enlightenment - the infinite wisdom and the opposite of knowledge.

True wisdom is letting go. The worst thing you can do to be wise is trying to be wise.