NLP. Its like this. You are a little kid, and your dog gets run over by a garbage truck at the same time a flock of birds fly over your head. Their wings and squaks cause so much noise, you look up at the same time your dog is hit.
Years later, you can't stand birds, but you don't know why.
Your unconscious relates the birds to the incident in which your dog was killed, but unless you have a way to remember this, it stays buried in your unconscious, and you fear birds. You might not like trash trucks either.