If you retreat at every challenge, you'll never make progress.
Tips
history
From 《左传·宣公十二年》: '见可而行,知难而退,军之善政也' — 'to advance when you see opportunity and retreat when you see difficulty is good military strategy.' Originally a neutral tactical principle; modern usage often tilts negative ('give up too easily').
usage
Context-dependent tone. Praising: 'wise to know your limits.' Criticizing: 'quits at the first sign of trouble.' Contrast with 迎难而上 (to rise to the challenge), its opposite.