It's a developmental phenomenon that occurs throughout early life. I like to think that the whole first half of life is really devoted to figuring out how to develop the independence and the success and the achievement that we're conditioned to pursue, at least in our culture. At lot of the information about what is okay to be and what feels good comes from one's peers. There's a great deal of baby being thrown out with bath water . . . Well, of course.
Most people project their Shadow onto others rather than really taking ownership of it.
The way to de-potentiate acting out or becoming one's Shadow is to own it, to see it not just as a mote in the other person's eye. I think holding them in check is only part of the process but yet, Shadow refers to the parts of us that are inferior and are undeveloped and need to be morally developed. There are also positive things hidden the in the Shadow. I like to think that a lot of people's real, natural gifts and talents may be caught in the Shadow because there was no one who really recognized and supported and nurtured these native talents. So there is gold in the Shadow.