So the thing about Icons is that they
do have an external perspective factor to them in canon, though how important that is isn't strictly defined in canon as you
do still need a personal revelation/enlightenment set up to pull it off.
I highly recommend reading the Cradle series and seeing the first on screen Sage Advancement we see as that and the build up to it should demonstrate the process pretty well.
It all comes down to the underlying Personal Power mechanism of
that the greater Way seems to operate on really.