The more refined our conscious personality, the more shadow we have built up on the other side. The ego and the shadow come from the same source and exactly balance each other. Without a working awareness of both ego and shadow we feel unbalanced--as if something is missing. A faint awareness that we're not completely whole. Remember Peter Pan? His shadow was on the loose. He needed help sewing it back on. We're just not complete without the balance of our shadow self.
Shadow has a bad rep--but it's not a bad thing. It's actually a gift. Shadow is everything that didn't find a place for one reason or another, and it got stuffed in the basement of our personality. The problem is that it won't stay in the basement forever, and will at some time (and probably not a convenient time) come knocking at the door. If you open the door and befriend what was formerly unacceptable about yourself, a lot of creativity and relief bubbles to the surface. Carl Jung called the shadow "pure gold".
So how do you know if you have shadow knocking at the door? Not complicated at all. If you have something that you can't manage, no matter how hard you have tried to kick it--it's probably shadow. If you are often frustrated or angry with someone else-- it's probably shadow. We often project our shadow onto others and get angry with it. The old AA saying, "if you spot it, you got it" is humorously accurate. Shadow is running the program unless you take some time to sit down, process it, and find out why it's there. We have to use it, not let it use us. If you think you might be having a struggle with this, talk to someone. Shadow will behave autonomously (operating independently) until you make it conscious by talking it through.
To own one's shadow is to reach a holy place--an inner center--not attainable in any other way. To fail this is to miss one's own sainthood--and the chance to find at your center pure gold.