Translators should not translate verse 21 until they have worked through the problems of both verses 21 and 22.

Do not be overconfident on a smooth way: The first problem is the meaning of the Greek word translated smooth. It is an extremely rare word, whose meaning can only be guessed at from its elements. In one derivation it means “smooth, having nothing to stumble over.” In another derivation it means “unexplored” or “untried” (An American Translation). Frankly, this latter meaning is more convincing to us. We think this verse means “Always be alert in unfamiliar territory.” Unfortunately the Hebrew is of no help, as will be seen in the next verse, where the problem involved in this verse gets deeper.

Quoted with permission from Bullard, Roger A. and Hatton, Howard A. A Handbook on Sirach. (UBS Helps for Translators). New York: UBS, 2008. For this and other handbooks for translators see here.