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

One of his first challenges was to change a helpless, can't-do mentality.

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And, I mean, to sit there on a bed and hear this and felt helpless that I couldn't help...

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The helpless man in a red T-shirt is dragged along the road.

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