In nature, there are certain patterns which can be observed. The ancient Indians identified three modes or qualities which can be applied to everything from people, food to behavior: sattva (peaceful), rajas (agitated) and tamas (dull).
In the Bhagavad Gita, Krishna indicates to Arjuna that the early portion of the ancient Indian texts, the Vedas, mainly deal with the three modes of nature. The way to overcome the limitations poised by these modes is to perform the Vedic duties without desire. To be situated in the mode of sattva, one needs to be self-collected without excessive worry about oneself in the manner of a hypochondriac.
trai-guṇya-viṣhayā vedā nistrai-guṇyo bhavārjuna
nirdvandvo nitya-sattva-stho niryoga-kṣhema ātmavān
This can be roughly translated to:
O Arjuna, the Vedas have the three qualities as their object. You become free from worldliness, free from the pairs of duality, ever-poised in the quality of sattva, without (the desire for) acquisition and protection, and self-collected.
– Bhagavad Gita, 2.45