Bhagavad Gita · Chapter 14: The Three Qualities of Nature

Bhagavad Gita 14.9

sattvaṃ sukhe sañjayati rajaḥ karmaṇi bhārata | jñānamāvṛtya tu tamaḥ pramāde sañjayatyuta ||

Clarity attaches a person to happiness, and passion to action, Arjuna. Inertia, veiling knowledge, attaches a person to carelessness.

Modern context

A simple summary: sattva ties us to happiness, rajas to action, tamas to carelessness. Each has its own pull. It is useful to know which pull is strongest in us. A person caught in sattva may avoid hard truths to keep feeling good. A person caught in rajas cannot stop working. A person caught in tamas cannot start. Each needs a different remedy.