Everything Changes, is it Really True?

" Fair is foul, and foul is fair". Those are the famous words involved and written by William Shakespeare in his book Macbeth. These words were said by the three witches as they suddenly appeared while they were walking. Even just simple words of the three witches affected the good-looking and kind man with a name of Macbeth. What do this words exactly mean?
In my opinion, let us define what is fair and what is foul in our life. Most of us think that our life is nothing but a game against each other. Being fair is something that we will not do anything just to profit himself against others. But, foul is nothing but a contradictory to being fair. He will do everything even doing worse things expected by our minds. The only goal to his life is nothing but to take an advantage to others he considers as an enemy.
What is that quote exactly means? For my opinion, it tells us that even a good person can be affected by the words and opinions by other persons. They will slowly be consumed by greediness and their belief will be different. As what was said, that person might think that being fair is not enough or is not right for a person to believe because as what I've said, their only goal is to reach the top even if the consequence will affect others. Also, they will think that taking advantage to others is nothing but a self-nature of himself since he will think that it's alright or it's just a part of the game of his life.
Even mere words can actually affect someones mind who focuses on achieving more of his goals, mostly those that set their minds in this goal. The only way to prevent thinking that thing is in ourselves. Neither someone can help you understanding those things. Only you yourself can find the answers that lies within you.