لَا يُقِيمُ الْعَزِيزُ بِالْبَلَدِ السَّهْلِ وَلَا يَنْفَعُ الذَّلِيلَ النَّجَاءُ
Meaning: Even a powerful person cannot remain secure on the open plain, and swift flight brings no benefit to one already overcome.
Here al-najāʾ means rapid escape rather than salvation in a general moral sense. Al-balad al-sahl is the open plain, with little shelter. Remaining and fleeing are presented as equally ineffective.
The parallel negatives lā yuqīmu / lā yanfaʿu give the assertion force. This is an intentionally sweeping military boast, not a literal rule about every journey or encounter.