Foxes, when they cannot reach the grapes, say they are not ripe.

People may disparage something only after discovering that they cannot obtain it. Calling the unavailable thing undesirable protects pride by turning frustration into apparent indifference.

The saying cautions against taking such criticism at face value. A judgment that something has little value may reflect disappointment or exclusion rather than a balanced assessment of the thing itself.

Use it when someone dismisses a desired opportunity, possession, or achievement after failing to secure it. It can describe self-justifying reactions, but may sound teasing, accusatory, or unsympathetic when addressed directly to someone whose disappointment is genuine.