Someone says "Something cannot be overemphasized means extremely important". Is that correct? If so, why?

To emphasise = to give importance to something

"It's so important, I mean incredibly important, you don't forget moms birthday, your life depends on it!"

"Ok, I get it, no need to overemphasise it"

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Thank you, Graeme.But I still don't understand it.

Thank you so much,Paul.