According to a documentary I saw, our instinct is developed by our experience. In the documentary, they compared how firefighters and an average guy extinguishes fire. Off course the firefighter were a lot better under the stressed conditions. The firefighter said that he did it based on his instincts. The documentary concluded that his instincts could be the result of his years of experience which enabled him to make very quick decisions without thinking for too long.
I trust my instincts base on the same reason too.