Bhagavad Gita, Chapter 14, Verse 10

Sattva arises, O descendant of Bharata, predominating over Rajas and Tamas; and Rajas over Sattva and Tamas; so, Tamas over Sattva and Rajas.

None of these three forces is described here as permanent, real dominance keeps shifting between them.

Krishna names this as an ongoing real competition, not a fixed state a person settles into once. Understanding the guṇas means understanding that the balance keeps moving.