Musar על פסחים 16:21

The general principle to distinguish between the two types of fear is as our sages specified saying: "where harm is likely it is different" (Pesachim 8b).

If a rabbi and Pious Man is far from his city he should not hold himself back from going there to study because of his fear of the roads, as does the lazy man who excuses himself by saying "There is a lion without; I shall be slain in the streets" (Prov. 22:13). But a man should keep in mind that many people travel and are not injured. So he too should not restrain himself from the journey out of fear, for those who are sent to fulfill a command of the Torah are not injured (Pesahim 8b).