Hope is an affective relationship with respect to an unknown future. Similarly, nostalgia is an effective relationship with respect to a fragmented past.
If the mind, our reasoning self, fails to understand other realities beyond that which we live right now, it is our affections that are moved by a nostalgic relationship with respect to a past and a hope in the future that allows us to turn to imagined scenarios of reinvention of the present.
Although nostalgia and hope can be used as excuses to disconnect from the present by the belief that "no new can be good enough" or that "the old is obsolete", it is that affective potential to understand what is already here or what is not yet here what is really radical.