Lie-san: (un-)important things

Slytherin's cardinal traits are ambition, cunning and determination. Like the Gryffindor House, Slytherins are emotionally volatile. In contrast, however, Slytherins are much less dominant and assertive, and less extraverted in general. Rather than expressing these emotions outwardly, Slytherins direct them inward or act in a passive aggressive manner. Both Gryffindor and Slytherin are much more driven to succeed than the other two houses: Gryffindor out of pride and Slytherin out of ambition.

Slytherins are also much more pragmatic than the other houses and more adept at manipulating people. A key trait would be a low level of agreeableness: Slytherins are more pessimistic, more distrustful than most, and more likely to attribute negative motivations to people. So although Slytherins experience a wide range of emotions, due to their distrustful views of people and skeptical worldview, they are less expressive and more likely to appear cold or distant unless provoked.

A Slytherin's ambitious nature comes out in different ways depending on what is important to the individual person. It could lead them to try to achieve top marks (if intellect and schooling is important to them) but it could also be directed at social settings or towards athletic endeavors.