When Buddhi becomes the master of Manas and Ahamkaar, that is when the evolution to your higher self begins and Yog becomes a becomes a real possibility.
Then it is no longer an unattainable ideal, but a difficult to reach (though not impossible) state of mature discriminating full brain thought and decision making.
Buddhi is the discriminating, mature intellect, the higher order thinking that, when working right, leads to Viveka or wisdom in everyday language.
