Literally: not – lose / error – correct – swan
Alternately: To correctly grasp the main point, meaning, or implication of something. To hit the nail on the head; to get a metaphorical bullseye.
Notes: This is a compound of compounds. 不失 refers to “not missing,” and 正鵠 refers to the center of an archery target, apparently so named because in traditional archery practice, one style of target has a central dot that is white.
The character 鵠 may occasionally be pronounced as kou without any change in meaning. The phrase as a whole may be given the Japanese-style reading 正鵠を失わず (seikoku wo ushinawazu), “to not miss the bullseye.”