From Ben

Wyvernian the TAOH cast actually come straight from Chapter 40. So they do have a bit more experience on the island (although that doesnt change the fact they still dont know what those dragons are) I also wouldnt say Samuel isnt desensitived to fear, he merely mastered his will to think rationally in any situation, no matter how dangerous (something he picked up from his past). He CAN feel fear however, in Chapter 13a when he was almost killed by a raptor he felt fear. So near NEAR death experiences can scare him, but the only time he felt irrational fear. (paranoia even) is when he spots the red haze stalking him. Then he begins to freak out internally even though it poses no threat to him.