How people find out about you matters a lot. Your current physician probably didn’t cold call you.
You find good products and services through recommendations, media, and searches. Anyone who is cold calling you is implicitly telling you, “Not enough people trust me to do business with me yet.”
That’s why cold calling is difficult. That doesn’t mean it’s impossible; however, it does mean that the fact that you cold called sets the tone of the relationship. The customer is taking a chance on you, and they will not be so easy to sway or influence. In services, this will influence the working relationship, which will in turn influence the success of the project.
That doesn’t mean you shouldn’t cold call or knock on any doors; it just means you need to choose the doors you knock on more carefully.
Sometimes, those doors might not belong to your customers. You may be better off spending extra time looking for opportunities to demonstrate your expertise and skills, and making media out of it, or to offer insights to people who need it.