The morning sun never lasts a day.

Bright conditions at the beginning are not guaranteed to continue. The saying advises against treating an early success, favourable mood, or promising start as if it assured a lasting outcome.

It evokes the short life of freshness and advantage: what is vivid at dawn changes as the day advances. It expresses a general idea of impermanence, without specifying exactly what kind of benefit or promise will fade.

Use it as a reflective warning when an initially encouraging situation may be temporary, such as a burst of popularity, an easy beginning, or a period of good fortune. Its image gives the remark a calm, cautionary tone rather than a precise prediction.