Siddhartha question

Early in the book, Siddhartha is observing Gautama. He sees Gautama sitting under the Bodhi tree. Siddhartha questions why. He infers that “He had heard a voice, a voice in his own heart which commanded him to seek rest under that tree, and he preferred neither mortification” [...] “So to obey, not an external command, only the voice, to be ready in that way, this was good, this was necessary, nothing else was necessary.”(41). Personal identity is one of the many themes in the book. We see Siddhartha trying to show everyone that they can make their own path. For our sake, how do we know what is necessary for our path and the choices we make to get on it?