他因没有仔细核对数据而犯了一个致命错误。

He made a ___fatal error by not double-checking the data.

她的致命错误是低估了这次考试的重要性。

Her ___fatal mistake was underestimating the importance of the exam.

公司的致命决策导致了其破产。

The company's ___fatal decision led to its bankruptcy.