In the new Poe Damerom comic we see Rey asking C3PO to translate the Jedi Texts that she had taken from the tree. The very first translation is - "The Force is the Light , The Force is the Dark , The Jedi chose the Light for all it reveals." Most fans I have spoken to over the years believe that the Jedi became more flawed over the years. That as time passed the essence of the core Teachings was lost and replaced by a focus on politics and maintaining the Republic. However, it seems that the Jedi, At least in the new cannon, made a deliberate choice to ignore one entire half of he Force. To me, this would be like focusing solely on general relativity while completely ignoring the quantum world and then wondering why your real world efforts to understand what is occurring around you continue to fail. So, if looked at from this perspective, the old Jedi order was doomed to fail from the very start. Taken a step further, if Luke had this realization while on the Island it could very well explain his mental and emotional state when Rey found him.