Foot in the door: “a persuasion method [in which] the persuader does something small in order to catch the target's interest, before moving on to what he really wants…. refers to the stereotype of a pushy door to door salesman inserting his foot in someone's front door so they become unable to close it and terminate the conversation" (Wikipedia)Just-world phenomenon: also called the just-world theory, just-world fallacy, just-world effect, or just-world hypothesis, refers to the tendency for people to believe that the world is “just” and so therefore people "get what they deserve." (Wikipedia).
cognitive dissonance theory: a tendency for individuals to seek consistency among beliefs and opinions, and to eliminate the inconsistency (dissonance) through a change in those beliefs or attititudes. Educational psychologists understand this state of cognitive dissonance as fundamental to the process of learning.
Group polarization: after participating in a discussion group, members tend to advocate more extreme positions and call for riskier courses of action than individuals who did not participate in any such discussion. Example: attitudes such as as racial prejudice tend to be reduced (for already low-prejudice individuals) and inflated (for already high-prejudice individuals) after group discussion. (Wikipedia)