Simplify the following text for a Grade 8 native English-speaking person.
Original: Freud has been influential in two related but distinct ways : he simultaneously developed a theory of the human mind 's organization and internal operations and a theory that human behavior both conditions and results from how the mind is organized .
Simplified: Freud developed a theory of the human mind ( its organization and operations ) . He also had a theory that human behavior both conditions and results from how the mind is organised .