Answer:
The answer to this is by putting the characters in an non-realistic and non-believable setting.
Macbeth at the beginning of the play is described as being valiant and worthy. He executes an enemy to protect his country from a rebel. At the end of the play, Macbeth's actions are similar (his instinct to fight and kill), but his justification for those actions have changed drastically. He decides to kill Macduff's family even though they have done nothing wrong, which is very different from his earlier willingness to kill an enemy in defense.
