It's the same concept in mental and emotional health."What you put into your mind is what you get out". If you feed your mind with worry, fear, anger, with no self-discipline you will lose control over your mind and emotions. Your spirit gets agitated and you lose balance.
This reminds of a story I read awhile ago and I am going to share it here:
THE TWO WOLVESA young boy came to his grandfather, filled with anger at another boy who had done him injustice.
The grandfather said to his grandson, let me tell you a story:
"I too, at times, have felt a great hate for those that have taken so much with no sorrow for what they do. But hate wears you down, and hate does not hurt your enemy . Hate is like taking poison and wishing your enemy would die. I have struggled with these feeling many times.
It is as if there are two wolves inside me, one wolf is good and does no harm. he lives in harmony all around him and doesn't take offense when no offense is intended. He will only fight when it is right to do so and in the right way. The other wolf is full of anger and the smallest thing will set him into a fit of temper. He fights everyone all the time, for no reason. He cannot think because his anger and hate are so great. It is helpless anger because his anger will change nothing. Sometimes it is hare to live with these two wolves inside me, because both of the wolves try to dominate my spirit."
The boy looked intently into his grandfather's eyes and asked,
"Which one will win, grandfather?"
The grandfather smiled and said , "The one I feed."