I told you! … mà at the end

At the end of a statement, mà insists. You use it when someone doubts you, has forgotten, or doesn't see what you see: Em nói rồi mà! I told you! Ngon mà, chị ăn thử đi. It really is good, try it. In English you'd stress a word, or add "really" or "I told you".

It often answers a question with a reason that should be obvious: Sao em không ăn? Em ăn rồi mà. Why aren't you eating? I've already eaten! It also reassures: Không sao mà. It's fine, really.

The tone does a lot of the work. Said softly, it's warm and reassuring; said sharply, it can sound impatient. With older people, keep it gentle and add dạ and their word: Dạ, con làm rồi mà mẹ. I've already done it, Mum.

Chứ at the end is the happy "of course" when someone asks: Ngon không? Ngon chứ! Mà pushes back against a doubt: Ngon mà! At the start of a sentence, Mà does a different job: "but" or "by the way".