I'm thinking Bellamarie we need both - like as in life - we look forward to a relaxing weekend and yet, if we do not challenge ourselves in our work we are not growing and able to provide more service to those who benefit from our work -
I think that our brain needs that same cycle - a time to relax with what is mediocre (synonyms: ordinary, average, middling, middle-of-the-road, uninspired, undistinguished, indifferent, unexceptional, unexciting, unremarkable, run-of-the-mill, pedestrian, prosaic, lackluster, forgettable, amateur) what would we do without amateur stage productions in our community or a school band or those who home sew - we are not all creating what is museum worthy and yet, how small our life if we choose never to visit and understand museum worthy art or hear live the symphony or a jazz band or see a movie with professional actors, much less have the good fortune to see a Broadway play that is a road production playing in a nearby community.
And so like reading - a cozy mystery or a current story that we will not see included among the list of literature studied in years to come, balanced by reading a bit of literature written either in the past or by a current author that challenges us to examine not only plot but structure and analogies that push us deeper into the story and its associations to life.
I do not think it is one or the other but both - just like we do not listen to all hip hop or rap music and ignore other genre - we know what is easy listening but we do not want to exclusively hear 'elevator' music and only listen to our favorites - if so we would never have any 'new' music - if we were stuck in music from the 70s or 80s we would never be able to enjoy a musical play like Hamilton.
I think all she is saying is how to define mediocrity which is reading that makes us feel cozy - I smile remembering how cozy I felt seeing my children and grandchildren on stage or playing in the annual recital or even being included in a special evening at a nice restaurant during the holidays where someone dressed with an old top hat read Dickens as we were served a typical Victorian menu. All warm and cozy as compared to seeing the stage production of "Les Miz" or even the movie version.