Superman was invulnerable. No weapons could harm him. This is similar to how WE become when we become convinced that our actions or other people’s opinions or criticisms have NO influence on how good/righteous/loved/approved we actually are. Our goodness/righteousness/loved-ness is established by the COMMAND of God, not by our actions or other peoples’ opinions (including our own) of us. The more we believe this, bullets (accusations/criticisms/negative judgements, etc.) more and more just bounce off. But few of us believe that we are invulnerable. Only then can you get the benefit. We can discuss this more if you like.
Now, if we could only learn to fly, too.