To be a good portrait photographer, you of course need to have solid lighting and shooting skills, but that's not all of it. Being a great portraitist take a strong ability to connect with your subjects, and this great video investigates why empathy is the key to doing that.
Coming to you from Sean Tucker, this wonderfully insightful video examines the concept of empathy and how it applies to portrait photography. A big part of shooting a portrait is successfully engaging with your subject to make them feel comfortable in front of the lens. Empathy is so important because it's a higher level of engagement than sympathy. Whereas sympathy is the act of caring about the feelings of one another, empathy is actually feeling those feelings, and when you do that, you better understand your subject as an individual, and that in turn makes you better able to represent their essence as a human being in a photograph. I think Tucker is really on to something in recommending photographers regularly get their own portraits taken as well. When you spend all your time behind the camera, it can be easy to forget what it's like to be in front of it, and that in turn diminishes your capacity for empathy. Getting in front of it regularly helps you to understand and remember the experience.