out of one's depth

Idioms  

1. Also, beyond one's depth. Outside one's understanding or competence, as in He was out of his depth in that advanced calculus class, or The conductor realized that playing the fugue at the right tempo was beyond their depth. This expression alludes to being in water so deep that one might sink. [c. 1600] Also see over one's head.

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Example Sentences

The issue takes on a special coloration when the topic under discussion is literally a matter of life or death and when being out of one’s depth can have serious consequences.

From Washington Post

Being out of one’s depth is an inevitable fate for a Henry Green character.

From The New Yorker

Depth′less, having no depth.—Out of one's depth, in water where one cannot touch bottom: in water too deep for one's safety: beyond one's faculties.—The depths, the lowest pitch of humiliation and misery.

From Project Gutenberg

The beach is very steep; and as one gets out of one's depth immediately, indifferent swimmers put on a couple of bladders—which stick out behind their backs and produce a strange effect—or else take a bathing-man into the water with them.

From Project Gutenberg

Adv. beyond one's depth, out of one's depth; over head and ears; mark twine, mark twain.

From Project Gutenberg