Dogged pursuit of a rabbi

Twice in the first chapter of Avot (1:6 and 1:16) we are told aseh lecha rav -- make, get or appoint for yourself a rabbi. Reading through the commentaries, it appears that there many explanations as to why Rabbi Yehudah HaNasi should have thought it necessary to include the same advice twice. Here's another explanation: one needs one sort of rav for one's youth but a different sort for one's old age.

In one's youth, when still learning Torah and/or how to handle life, the advice of one's elders is generally essential, if not always welcome. The rav (rabbi, teacher) can fill in the gaps in one's knowledge and help cultivate a better understanding of the world and its challenges. The typical profile of the rav is that of an older, wiser persona, someone who can supplement and balance the more intimate input of one's parents by providing greater objectivity.

In one's old age the position is quite different.  Most of the wisdom one needs in order to navigate life has been acquired and very probably put into effect, and the issues and uncertainties that accompany every step in one's path through youth and middle age have been replaced by the certainties of retirement and gentle decline. Such a person may have no obvious need for the guidance and instruction of a teacher. However, the mishnah teaches that the need for a rav is no less great. How so?

Training for the rabbinate?

If one can draw an analogy, the rav in one's later years is rather like a guide dog for a blind person. The guide dog may not have much input in its owner's intellectual and moral development, but it can stop its owner walking in front of passing traffic or stepping off the embankment and falling into the river. This sort of input is vital -- and the dog must be alert to the blind man's needs and to act without being prompted when action is required.  These are also the qualities of the rav in one's senior years: to be able to keep his talmid morally and halachically safe and sound -- and to be able to do so in a tactful manner without being asked.