Freud released "Beyond the Pleasure Principle" in 1920 and it talked about the different instincts that humans experience and how they affect our behaviour.

For Sigmund Freud, instincts are the principal motivating forces in the mental realm, and our instincts can be grouped into two broad generic categories, Eros (the life instinct), which covers all of the self preserving sex stuff, and Thanatos (the death instinct), which covers all the aggressive, self destructive, cruel instincts.

Freud said "So, after many years of investigation, I have proposed two fundamental aims: life and death, which I named in honor of those immortals, Eros and Thanatos."

Freud believed that in order to relieve the tension between Eros and Thanatos, humans must be aggressive, This theory suggests then that aggressive behaviour is a necessary act in order to decrease the tension as to prevent the destruction of the individual. Freud claimed that small aggressive acts allow people to release some of the tension so it is not able to build and mount to anything substantial