Medlars are never good till they be rotten.

Some things attain their proper value only after an unpromising stage of decline or delay. The saying draws on the traditional idea that medlars become edible only after pronounced softening, turning apparent spoilage into a condition of readiness.

Figuratively, it can counsel patience with something that seems past its best, awkward, or unsuccessful at first. Its point is not that all neglect, damage, or decay is beneficial, but that apparent deterioration may sometimes precede usefulness, sweetness, or maturity.

Use it humorously or reflectively when time, aging, or an initially disappointing process makes something better suited to its purpose. Because the image is blunt, it suits self-deprecating remarks about late improvement or delayed appreciation, not claims that deterioration will reliably make things better.