千虑一失

reflect a thousand times and you can still make a mistake (idiom); to err is human

thousand

see 鞦韆|秋千[qiu1 qian1]

to think over / to consider / anxiety

one / single / a (article) / as soon as / entire; whole; all; throughout / "one" radical in Chinese characters (Kangxi radical 1) / also pr. [yao1] for greater clarity when spelling out numbers digit by digit

to lose / to miss / to fail