To be vulnerable means exposing yourself to the world and freely and courageously embodying your authentic persona.
But it also means that you open yourself to people with malicious intent and a pessimistic worldview (the same people who regard dialogues as debates instead of an exchange of ideas and interpersonal problems as a battleground instead of an opportunity to grow).
For instance, you might tell your romantic partner that you want to feel appreciated. In this act of vulnerability, you end up either connecting more deeply with your partner or risk having them take advantage of you (consciously or not).
To offset the downside, seek to be vulnerable but impenetrable. Accept the risk, and, if needs be, stoically accept the consequences. Trust that, on net, the value in a deeper connection with the world is worth the risk. Ensure that should your vulnerability be taken advantage of, your self is resilient and robust enough to withstand the storm.