Meaning:

To tell people that you will not help them even though they need your help very badly

Example:

Sarah and Jack are friends. Sarah is very good at math, but Jack thinks math is very hard. They have a test coming up tomorrow. Jack is very nervous because he thinks he will fail, and the test is very important. He decides to ask Sarah for help.

"Sarah, will you help me study for the math test? I don't understand how to do the problems."

"I'm sorry," Sarah answers. "I have to baby-sit my little brother tonight, so I can't help you study."

"How can you turn your back on me when I need you so much? I'm going to fail this test if you don't help me," Jack says.

"I'm sorry. I can't help you tonight because I am busy."

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