Devas gain rebirth in the heavenly realms through accumulated merit, particularly acts of generosity — and experience correspondingly vast lifespans and refined pleasures, with the lowest heaven's inhabitants measuring a single day and night in fifty human years. Yet Buddhist teaching is emphatic that this is not liberation: devas are still fully inside samsara, still subject to old age and death when their store of merit is exhausted, and their downfall is traditionally marked by five ominous signs — soiled clothing, fading garlands, sudden sweating, an unaccustomed foul odour, and a creeping unease with their own heavenly seat.
The deeper critique, repeated across the tradition, is that the very comfort of the deva realms is a spiritual liability: their inhabitants' pleasure and longevity blind them to the First Noble Truth of suffering in a way the harder human realm, paradoxically, does not — which is why Buddhist teaching consistently ranks human rebirth as the most valuable and workable state for pursuing liberation, not the heavens above it.