One of the most challenging kind of photography (to me) is portraiture. You have to concern a lot of things technically, especially in matters of light. The light may not be to harsh right in the face. The model could narrow the eyes to slits or the skin shines. When the light comes from above directly, you get shadows under the eyes, wich makes you look old or tired. If the light comes from below, it makes you look kind of scary.
If you shoot a woman, you need softer light in order to flatter her skin. With harder light you can make a male model look more masculine.
There are so many things, you must take care about. You also have to think of the background and the clothes of the model. And what makes me nervous is, that there is someone in front of the camera who is waiting, that i take the picture. I can not take time like i can, when i shoot a static object.
Then you have to give instruction and entertain your model, in order not to get bored. That would cause an equal facial expression. Furthermore you have a pressure to deliver, because there is a person who has certain expectations in the results.
All these issues are the reason, that i don’t have much portrait photos in my stock yet and it will never be my preferred genre. But maybe i will participate a workshop one day to become safer.