There is no great psychological mystery around critical people. They feel bad about themselves and their lives. Their critical attitude is a projection, a way to try to make others feel bad about themselves too in order to transfer some of that built up unpleasant psychic pressure.
The reason this strategy works is that there often is some truth in their criticisms. They prey upon those in the process of self-actualization, those who are putting effort into their own growth and aren’t as polished as they will one day be. This is why if you are walking the path of self-actualization you shouldn’t worry too much about critiques of what you’re doing because your outlook is one of open learning and their outlook is one of closed judgment, two outlooks that are incompatible with one another and that come from completely different psychological places.
It’s infinitely easier to destroy than it is to build. Critical people love destroying the hopes and aspirations of others because their own hopes and aspirations have stalled. Don’t succumb to the temptation to join them by giving up or becoming critical yourself. Let critical people deal with their own baggage instead of shouldering some of the burden for them.
This doesn’t mean that you shouldn’t listen to constructive feedback, but there’s a qualitative difference between constructive feedback and the critical behavior we’re talking about. People who give constructive feedback believe you are capable of improvement and want to help you get there whereas critical people see you as stagnant because they see themselves as stagnant, and so they treat the various manifestations of your self-actualization as such.