Different people tell different things. Barely anyone knows the truth...
"Know thyself"
~Plato~
"No man is free who is not master of himself"
~Epictetus~
"Man is disturbed not by things, but by the views he takes of them."
~Epictetus~
Some quotes by Marcus Aurelius
"He who lives in harmony with himself lives in harmony with the universe."
"The universe is change; our life is what our thoughts make it."
"Such as are your habitual thoughts, such also will be the character of your mind; for the soul is dyed by the thoughts."
You have power over your mind - not outside events. Realize this, and you will find strength.
"Very little is needed to make a happy life; it is all within yourself, in your way of thinking."
"When you arise in the morning, think of what a precious privilege it is to be alive - to breathe, to think, to enjoy, to love."