"The greatest discovery of my generation is that human beings can alter their lives by altering their attitudes of mind."
~ William James
Two thousand years earlier, the Buddha said that
The thought manifests as the word;
The word manifests as the deed;
The deed develops into habit;
And habit hardens into character;
So watch the thought and its ways with care,
And let it spring from love
Born out of concern for all beings ...
Buddha, Dhammapad