Again (annoyingly), unexpectedly: lại before the verb

You know lại after a verb for "again, over": nói lại, say it again. Before the verb, lại adds a feeling. Often it's "again" when you didn't want it: Trời lại mưa rồi. It's raining again. Em lại quên chìa khóa nữa rồi. I've forgotten my keys again.

It also marks something as unexpected, against what you'd think, like "and yet" or "of all people": Nhà gần nhất mà anh ấy lại tới trễ nhất. He lives closest, yet he's the last to arrive. After còn, it sets one person's choice against another's: Em thích biển, còn anh Minh lại thích núi. I love the beach, but Minh prefers the mountains.

In questions, sao … lại asks "why on earth": Sao em lại khóc? Why are you crying?

Watch the place. After the verb, lại means doing something over, usually on purpose. Before the verb, it means something happens again, or happens at all, when you didn't expect or want it.