Are there mistakes? It depends on certain things.
For instance, someone assumes that they will keep breathing over and over, they do not think that perhaps their next breath will not come at all, that they will simply die right then and there (maybe from an aneurysm or some other sudden event) - they would say to themselves, "Oh! I do not know, but I must not think of such things, that would cause me to be filled with complications, and I cannot deal with it - I just want to be comfortable."
While another person does not assume they will keep breathing, they think that perhaps their next breath will not come at all, they they might simply die right then and there - they would say to themselves "Oh! I do not know, so I must think of such things, because that would cause me to realize every moment is infinitely precious, and I have no time to waste - I must live each moment to the fullest."
So which one is the mistake? It depends on your aim. It depends on what you want. It depends on your objective. Do you want to be comfortable in your routines, secure in your day-to-day life? Or do you want to live each moment to the fullest, and be free to do as you wish?
You assume the forest man is a normal human, that it is normal for him to think that way. You cannot learn from him, for you assume you already know him. Is that a mistake? It depends on your aim. It depends on what you want. It depends on your objective.