من راقب الناس لم يظفر بحاجته
Whoever constantly watches people's reactions does not attain his aim.
Bashshār contrasts excessive concern about public reaction with the boldness needed to pursue one's desire. The wording links monitoring others with failure to attain a goal.
The poetic point concerns the inhibiting effect of excessive social caution; it need not be converted into an unrestricted ethical endorsement of recklessness.