[quote=@Jig]
<Snipped quote by Tarquin>

I frequently see the "Character has [Personality trait X] but also is [Diametrically-Opposed Personality Trait Y] in some circumstances". I don't think it's meant to be a carte blanche but an attempt to balance the character and give them some dynamics - although, as you say, it does basically load that character with caprice in the very section that's supposed to make your character comprehensible and reasonably predictable for the GM (and usually other players') benefit.
[/quote]

It's less about having an opposing trait and more that the trait seems to be there specifically so they can dismiss the realities of certain situations. For instance, I'm used to this kind of personality cropping up in Naruto RPs. Naruto RPs usually involve 13-15 year old kiddies that are just getting involved in military work, which often involves killing real people. Now, surely you would agree that even fresh soldiers, especially if they happen to be kids, are not often completely detached from the process of killing people? And yet so many of these kiddies happen to be completely fine with filling people with sharp objects and burning them to death. Not even so much as a slither of apprehension in most cases. And then they go right back to being kind and full of empathy in spite of having recently turned a man into a blood fountain.

Maybe they're just playing into the spirit of anime a bit, but it really irks me how characters can be "READY TO DO WHAT THEY MUST" with little to explain how or why they became so coldly detached from killing people.