Before deciding to pursue an advanced degree in counseling, I was a human biology major in college. My favorite subject was neurobiology because to me, the brain is this beautiful concert of neuronal firings and neurochemicals that as Descartes described it: the essence of our being. In a small, 3-5 pound mass of organic matter, holds our self concept, our memories, our senses, and our world view, it also is a museum holding the artifacts of our evolutionary history. Specifically, the strongest ancestral instinct is the one for survival.
For example, a client with severe social anxiety could tell me that they get really anxious when friends ask them out, so much so that they just stay home alone. Digging a little deeper, I may find that this client was once a very sociable person, but then it all changed in high school when they were bullied and rejected by their peers. In this case, the client's brain may be telling the client "Hey remember how much that hurt, let's avoid that" and keeping the client where they feel safe. What if, however, the client did want to go out but was still unable to go out because of their anxiety and reports feeling stuck. In that case, the client recognizes the problem, but is unable to figure out how to shut down the survival instinct. Therefore the client perseverates and is unable to go out or even able to enjoy a night out with friends due to her fear of rejection or fear of feeling anxious. We see that the client's survival instinct has take over and her brain becomes frozen and unwilling to let the client go out due to fear and anxiety.
This is where psychotherapeutic interventions come into play. They first make the client aware of their actions and that what they are doing to avoid pain may actually be contributing to the problem rather than alleviating it. They understand why the maladaptive practices exist and learn new tactics and new coping mechanisms that help the client live the life that makes them happiest.
As we can see, the human survival instinct is a powerful and useful tool that protects us, but it can also get us into trouble if we let it run unchecked.