http://revach.net/article.php?id=4176

Section:  Avodah   Category: Pirkei Avos
Rav Eliyahu Lopian - When One Walks On A Lonely Path He Is Forfeiting His Life
The Mishna in Pirkei Avos (3:4) says "ViHaMihalech B'Derech Yichidi... Harei Zeh MisChayev BiNafsho", and he who walks on a path alone... he has forfeited his life."  What is so terrible about walking on a road all by yourself, that you would deserve death?

Rav Eliyahu Lopian in Lev Eliyahu says that this Mishna is not referring to a physical path, but rather a spiritual one.  We are fortunate enough to have a mesora in hashkafa from Gedolei Olam of previous generations.  There are many great seforim and living tzaddikim that tell us very clearly what our Avodas HaChaim is.  We are given clear boundaries what is for a Yid and what is not.

The Mishna is talking about a person who dismisses all this, saying that the Torah is given to everyone, and each individual can define the Torah as he sees fit.  A person brazen enough to dismiss the teachings and the ways of our heritage, and creates his own synthesis of various polluted hashkafos, paving his own lonely road and creating his own Torah, is Mischayev BiNafsho.