As We Think, So We Become

"The thought manifests as the word;

The word manifests as the deed;

The deed develops into habit;

And the habit into character.

So, watch the thought and its ways with care

And let it spring from love

Born out of concern for all Beings.

As the shadow follows the body,

As we think, so we become."

From the Dhammapada Sutra

Sayings of the Buddha

Collected around 100 CE