It was expected by leadership of interwar Poland that whole country could end occupied by Germans before Germany is defeated by France & UK in the West. So Poland unable to hold long enough to see Germans crushed by Western Allies was not surprise. Surprise was pace of German advance. In ww1 conditions country size of Poland should be able to hold on for months and repeat of ww1 style conflict was something expected by both Poles and Western Allies. If there was example of Blitzkrieg before invasion of Poland that way of thinking would be changed.