Everyone is struggling to gain something which he does not possess, and he’s lamenting for something which he has lost. But when he realizes himself that “I have nothing to gain and nothing to lose; I have nothing to do with this material world,” that is called brahma-bhutah. That is Brahman realization.

From Srila Prabhupada’s lecture on Srimad-Bhagavatam 1.2.30 — Vrndavana, November 9, 1972