In the teachings of the Bible, every one of God's Ten Commandments is supposed to be intrinsically hard for humans to obey. They stand in direct, equal opposition to mankind's primary flaws, which date back to the first two humans, Adam and Eve. The couple was expelled from the Garden of Eden after committing the first act of disobedience against God: eating from the Tree of Knowledge of Good and Evil. In committing the act, Adam and Eve gave all humans thereafter the desire to disobey God.
In real life (outside the Biblical abstraction), any of the Ten Commandments might be harder to obey than the others. Acts of deviance from defined rules, whether religious in nature or otherwise, vary according to the personality, history, and inclinations of each individual.