Poland was invaded on both sides, by the Germans and the Russians.
Yet they continued to fight, over the English skies, and at Monte Cassino.
I didn’t know about that narraitve until a “resistance fighter” came to our school system and gave a speech for the kids. What he actually did was help the Soviets conquer Poland. His claim was that he joined the Soviet army to drive the Nazi’s out of Poland. Because he labeled himself Jewish his story was accepted uncritically.
Poland was indefensible in 1939. Purely militarily the only defense was to fall back to the Vistula but that would give up the manufacturing base in the western half of the country. And East Prussia due north of Warsaw did not help either. Probably could have held at ww1 speeds but not motorized speeds.