Avot254

1:
It is rather difficult to identify Rabbi Nehorai. In
Avot 239 we had occasion to quote the Gemara [Eruvin 13b] where one opinion said that Rabbi Nehorai was a synonym for Rabbi Me'ir. However, this attempt at identification is rather spurious. The Gemara [Kiddushin 82b] quotes Rabbi Me'ir as saying that a person should always make sure that his son has learned 'a clean and easy trade'. On that same page of Gemara we find Rabbi Nehorai disagreeing with this teaching. Rabbi Nehorai says:

Unless he was halakhically schizophrenic it is most unlikely that both the adjacent teachings would have come from the same sage!

2:
Since the Gemara [Rosh ha-Shanah 22b] intimates Rabbi Nehorai as being a member of the Sanhedrin which convened in Usha after the Hadrianic persecutions he must have lived during the second half of the 2nd century CE. This sage is mentioned only three times in the Mishnah – and one of those is, of course, our present mishnah (and another has just been quoted above; the third is in Nazir 9:5). He is also occasionally quoted in baraitot (Tannaïtic material not found in the Mishnah). Most of these occurrences are aggadic in nature. In two places [Shabbat 60b and Nazir 5a], however, he deals with halakhah.

3:
We have often had occasion to note the fact that until the time of Rabbi Yehudah, the President of the Sanhedrin (around 200 CE), the Unwritten Torah was passed on orally had a great impact on the way in which Torah was studied and passed on from teacher to student and from generation to generation. And it is this consideration which underlies the teaching of Rabbi Nehorai in our present mishnah.

4:
If one wanted to study Torah one had to attach oneself to a teacher: it was not (and is not) possible to effectively study the Unwritten Torah with no external help. Thus, if there was no appropriate teacher in the place where one lived one would have to 'exile oneself' to a place where there was such a teacher. Already in the first chapter of this tractate [Avot 031] we learned that one should

to further one's studies. We must remember that since at this point in time the Oral Torah was not yet written down, learning Torah on one's own was, as I have intimated above, next to impossible. If one was fortunate one might have had a copy of the written Torah, but the Mishnah and all of the other compositions of the rabbis did not yet exist and even when they were compiled, they were learned orally.

5:
Rabbi Ovadya of Bertinoro, in his commentary on our present mishnah, follows this same line of thinking.

6:
Although in our day we have books and the Internet and one can learn Torah without a chavrutah (study companion), it is still far more effective to learn with a chavruta. In Avot 036 I wrote:

And this, of course, is the thrust of the last clause of our present mishnah, which is a direct quote from Proverbs 3:5 – 'Do not rely solely on your own understanding'.