Bhagavad Gita · Chapter 4: Knowledge and the Renouncing of Action

Bhagavad Gita 4.2

evaṃ paramparāprāptamimaṃ rājarṣayo viduḥ | sa kāleneha mahatā yogo naṣṭaḥ parantapa ||

Handed down in this way from one to the next, it was known to the royal sages. But over a long stretch of time, Arjuna, this yoga was lost to the world.

Modern context

Even the best teaching can be lost. No one destroys it. It fades through long neglect, when people repeat the words and stop living them. The same happens in a family, a craft or an institution: what the founders understood, the heirs only recite. Knowledge survives when each generation practises it. Books on a shelf do not keep it alive.