To appear suddenly and unexpectedly; to come out of the blue.
正当大家一筹莫展之际，一个奇妙的解决方案竟然从天而下，令问题迎刃而解。
Just as everyone was at their wit's end, a wonderful solution seemed to descend from the sky, resolving the problem with ease.
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To appear suddenly and unexpectedly; to come out of the blue.