Say, for example, an English teacher basically read the classics, romanticists and the moderns because her curriculum required it but, in fact, really only favored mediaeval literature. Let's say that in her view, the literary ideals and themes from that age were the only ones that knew how to portray true love, altruisim, gallantry, etc., etc.
Those preferences will tend to color her outlook on what others write. She will know very well what is cherished by others in writings from later ages but, for her, Mediaeval is the only worthwhile literary thing. She will fully understand and will be able to critique a modern stream of consciousness thing. She probably was able to understand and appreciate 70%(?) of the literary references of Joyce's Ulysses in one reading. BUT she will still view the work from that special lens of hers because of her preferences.
That's all I meant, really.