All lay load on the willing horse.

People tend to give extra tasks and responsibilities to the person who is dependable, cooperative, and least likely to refuse. Readiness to help can therefore attract a growing share of the work.

The saying also carries a caution: generosity and diligence may be taken for granted when others repeatedly rely on the same capable individual. It invites awareness of unfairly uneven burdens, rather than blaming willingness itself.

Use it when a reliable helper, employee, or family member is repeatedly assigned more work because they can be counted on. It can gently criticize an unequal division of labor or warn a helpful person to set limits.