With all of the other crew members you know who they are and where they stand on everything thing. But Spock goes though life denieing half of who he is. He talks about Vulcans do this, Vulcans do not do that. He never refer to his human side and the few times he does show his human side he mades up some story to cover it up. He placed his Vulcan side above humans while hiding & denieing his own human side. He is not being who he is unlike all the other crew members.