Usually, a son will walk humbly behind his father. By letting his father go first, the son demonstrates his respect for him.
However, if the path is muddy or blocked with branches, the son will insist on going first. This way he can clear the way for his father to follow after him.
Guarding Their Father's Honor
When Shechem and Chamor came to speak to Jacob about Shechem marrying Dinah, something unusual took place. Jacob was silent, and his sons spoke instead of him (Gen. 34:13). Why did they not show more respect for their father?
Ordinarily, Jacob's sons would never have spoken for their father. With the ugly incident of Dinah's kidnapping, however, they wanted to protect their father from having to be involved in the case. So the sons spoke instead of their father.
This is why the Torah emphasizes that the brothers spoke with mirmah, slyly - they calculated that it was necessary in this case to speak in their father's place. Like the respectful son leading his father through a muddy path, they saved their father from having to deal directly with this sordid business.
(Adapted from Mishlei Ya'akov, p. 81.)