I think this one has a few challenges, the hair covers some landmarks, and his right side is in shadow, hiding 3D information, note the subtle value changes and less subtle color changes of the lower lip to chin and how it can make judging the proportions harder, plus, his mouth is open (which is a little nightmare, especially when teeth show, as if you aren't careful with teeth they can look nightmare inducing XD), also the shape of his eyes feature prominent epicanthal folds and an almost almond or trapezoid shape.
cheers