«اِلْمَيَّهْ تِنْشِرِبْ مِنْ إِيدْ سَاقِيهَا»

The image is simple: a drink is best received from the person whose job it is to serve it, the one who hands out drinking water, not someone who irrigates land. From that picture the saying draws a general rule. Every task has someone who handles it properly, and things go well when that person is the one doing it.

The proverb also warns against swapping roles. Skill in one kind of work does not mean skill in all work; someone suited to one duty may fit another poorly. Water service is only the image: the point concerns fitness for any role, not a particular trade.

Use it when someone insists on doing a job outside their skill, or when praising the right person for a task. It can also gently explain why a capable person in one field should not automatically be given duties in another.