Struggle
They say that the biggest battle in a person's life is the battle against himself. Each individual has opposing and contrary desires within oneself that pull him constantly one way or another.
On a basic level, each person is trying to balance primitive animals' desires and moral consciences that dictate the right thing to do.
Both are part of one whole, and both coexist within a person, and a person struggles his entire life to balance these faculties.
Psychology breaks down the human mental state into three parts: id, ego, and super-ego.
Id is the primitive instinct part, the super-ego drive as a moral conscience, and the ego struggles to balance those two.