You use "I can't help but" when you feel helpless, when you want to get something across that needs to happen.

当你觉得无助时，或者当你说明需要做到这件事情的时候，你就可以使用“I can't help but”句型。

I can't help but 课堂 - SpeakingMax英语口语达人

Older men are known to get helpless high school crushes at the sight of beautiful younger women.

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Where do helpless students get the notion that intelligence is fixed?

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They had been helpless during the twister, unable to get to their kids, desperate.

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