Vulnerability is, to me, one of the highest levels of inner-strength, as counterintuitive as it may sound to most folks who have been trained so well to suppress their feelings and create an unauthentic persona, including my former self.
A trivial example might be apologizing quickly and sincerely whenever screwing things up! Apologizing is a vulnerable action. It means exposing oneself emotionally. It requires taking the risk of being rejected; thus, a high level of inner-security and a great deal of character strength.
People who can’t apologize or who offer shallow apologies, in best case scenario, are the weak ones, it seems to me. They are afraid of rejection or being taken advantage of. While the first group value is the bravery to do what seems right no matter the result, the second group one is the ego’s protection at all costs.