Patients want to make sure they are getting the best possible medical care, which is why they will often seek a second medical opinion. This is their right, and it's a sensible thing to do . After all, two heads are better than one, and the second opinion can actually increase their trust in you, if the doctor corroborates your advice. If he doesn't, then you have additional food for thought, and can use this as an opportunity to improve your treatment plan!
However, many doctors feel threatened when the patient ask for a second opinion. Is this because their ego is offended ? Or that they feel that this is a sign that the patient does not trust them ?