can't make head nor tail of (someone or something)

can't make head nor tail of (someone or something)

Cannot understand someone or something at all; cannot make any sense of someone or something. I've been working with the new software for hours, but I still can't make head nor tail of it. I can't make head nor tail of that new guy in accounting. Sometimes, he's really friendly, and then other times he acts like he's never met me before.
See also: head, make, nor, of, tail
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