Out of the blue

Meaning/Usage: Out of nowhere; spontaneously

Explanation: Although "blue" represents being sad, it is also commonly used to represent the ocean or the sky. Both are extremely big. If someone says to look for something that is in the sky or the ocean, there is no way to know where. Therefore, this phrase was created to represent coming out of nowhere.

"He's pretty funny because he will crack a funny joke out of the blue."
"Grace started crying for no reason. It was totally out of the blue."
"I don't know why he started getting mad. It was out of the blue."

A: "Did you hear what happened with Tiffany?"
B: "She broke up with her boyfriend last night."
A: "What? I thought they had a great relationship."
B: "So did I. It was totally out of the blue."

Other Common Sentences

"She showed up out of no where."
"He pulled a rabbit out of nowhere. That's why it was so impressive."