What does that mean? If you see your ex on the street, emotionally detached is not running away from her and not running toward her. If she says, "I'm going to Hawaii for vacation," it's not asking which island or deep details. It's saying, "That sounds nice." You care but you don't really care. You're emotionally detached.
Doing this for the whole world sounds easy but it's one of the hardest things you can possibly do. Imagine if a million people suddenly loved you. It's almost impossible not to feel elated. Now imagine if a million people suddenly hated you. It's almost equally impossible not to feel devastated. But you can do it; and if you do it, you can unlock true happiness, true freedom.
It's like this article says, but I don't see it about being an adult -- it's about being truly free.