The term "vulnerable" is used for someone who is susceptible to emotional or physical injury. Escaping physical injuries is possible by being careful and cautious in one's behavior and mannerisms. To stand emotional injuries, one has to be internally strong to take setbacks, criticism or any sort of moral attack. Living in a world which is full of weird and different personalities, you are bound to be the victim of moral attack and criticism. But you have to learn to pay attention to things that bother you. A critic is often like a lame man teaching others how to run.
All of us have some weaknesses or flaws in one's character. These weaknesses become our points of vulnerability. One should be intelligent enough not to let others know about our weak or vulnerable points. Our enemies and foes are bound to take advantage of our vulnerable points or Achilles-heel to let us down in public before others or to hurt us in person.