To be at one's wit's end; to have exhausted all one's wisdom and ability; to have nothing left in the tank (intellectually or skillfully).
面对这个复杂的难题，他冥思苦想，最终感到智尽能索，只好寻求他人的帮助。
Facing this complex problem, he racked his brain, but eventually felt he had exhausted all his wisdom and ability, and had no choice but to seek help from others.
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