With regard to the culture clashes in different nations and communities, use of the contact hypothesis theory could help to ease tensions.
In the contact hypothesis theory, which is credited to Gordon Allport, is the ability for two or more cultures to coexist peacefully through meaningful and thoughtful interaction in order to reduce prejudice. To ensure successful contact, it is recommended that: both groups receive equal status of importance with minimal differences in characteristics, backgrounds, and qualities; groups work towards achieving a common goal which is equally beneficial to both groups; there is cooperation from all subjects in each group; support from local authorities of laws/government and customs; personal interaction between members of opposing groups.
Potential outcomes for successful tourist-host contact include: relaxed attitudes, understanding, a mutual appreciation for the opposing culture's values, positive interactions wherein cultures are respected mutually, increased active communication to ensure both parties are satisfied and can co-exist peacefully, and perceiving the opposing culture as equally important.
Point out that your roommate has just experienced hindsight bias or the I knew it all along phenomenon.
Hindsight bias is the tendency to believe only after learning the outcome that one would have foreseen it beforehand. In simpler terms, hindsight bias is believing that you knew something only after you heard it or that you would've known it before hearing about it.
Hope this helps!
