I think every person is at a certain path in their growth cycle and while some are very serene, others are not there yet. They are hurt and frustrated and defensive and angry.
I was talking with someone about this recently, that it is like walking down a road and coming across an injured puppy. The puppy might snarl at you, but it is because he is injured and scared. He needs help and he doesn't know what to do or who to trust.
I know it's easy to get frustrated right back when someone is acting that way. It's human nature.
I try my best to realize that they are hurt and sad inside. Their outward expressions simply mirror their insides. They feel down about themselves and the thought of someone else succeeding makes them feel even worse. It's not a good state to be in. They need help, but they don't know how to ask for it. They feel stuck. And that makes them angry and frustrated.
So I try my best to be even more understanding, to be there if they need help, but also to gently distance myself from their harmful barking if there is nothing I can do immediately. That is, yes, they are hurt and they need to take steps to heal. But I can't "make" them heal - and while I can do my best, I also need to keep myself protected and not let myself be constantly abused in the process.