how can social cognition may both positively and negatively affect one's attitudes and behaviors?

Answer 1

http://en.wikipedia.org/wiki/Social_cognition

Answer 2

The schemas related to particular objects/events that you have can lead to respond to them negatively or positively.

http://www.google.com/search?client=safari&rls=en&q=schema&ie=UTF-8&oe=UTF-8