Chulin 7b: One does not stub his finger, unless this was decreed above. ¹

R. Yonah: After saying above that one should hope to Hashem to save him from all his fears (22), here it warns to cast on Hashem to make his ways succeed and bless his deeds. If one goes on the road or embarks on the sea to profit in business, often there is a loss in place of the gain that he hoped for. When he goes confidently, mishaps can occur. Therefore, "v'El Binasecha Al Tisha'en" (3:5); rather, put all your hope in Hashem.

Malbim: I explained above (16:9) that man chooses which path to go on - right or left - but motion of the legs is from Hashem and His power. He can stop someone from going in the path that they chose - "Lev Adam Yechashev Darko va'Shem Yachin Tza'ado" (16:9). Even if it seems to man that his path is good and he will he will agree to the good path according to his understanding, it will not help. It depends on Hashem to complete the action. Often this is hidden from man. Sometimes he sees an obstacle in his way and it seems bad. Really, his steps are from Hashem. What can man understand - his Tevunah is too small to understand!