There are a lot of topics from psychology that will have an impact on my even five years from now. From causation vs. correlation, to nature vs. nurture the list goes on and on, but the most influential would be The Big Five Theory of Personality. I think this theory stands out to me more than any because any human interaction that a person has will be influenced by this theory. Every person has a very distinct combination of openness, conscientiousness, extraversion, agreeableness, and neuroticism. When interacting with people its beneficial to identify which of these traits are the strongest, or weakest, to interact as best as possible with people. If you can get a decent grasp on what a person's traits are, you can then take from that certain behavioral traits and how their culture has influenced them. It's important not to approach every single person the same way but to treat each person differently and respect differences in personality. As a result of how many times in a given time you interact with people I see myself applying this theory the most five years from now.