Some people define “vulnerable” as being subject to attack or invasion, such as a military defensive position, or a weak aspect of a sports team (the Buccaneers’ defensive secondary was their vulnerability all season).
However, allowing yourself to be emotionally vulnerable is to maturely and intelligently listen to and accept others’ opinions and feedback. While unsolicited feedback is usually worthless and from people who simply can’t do things as well as you can, solicited feedback from people you trust can help you to grow. But that requires that you do not try to “shore up” you defenses, as if you are protecting the coast or a lead in a game.
I’ve know a lot of people who are ingenious at defending themselves and repelling all attempts to listen to helpful advice from people who really want to help them. They haven’t budged from the coasts.
Of course, all the action, meanwhile, is inland.