On this day 1939 the Soviet Union invaded Poland during World War II, more than two weeks after Nazi Germany had launched its assault.
I guess the other half supported the Nazi invasion of Russia - which was going to happen with or without the agreement.
From what I’ve read Poland rebuffed any suggestion of a joint defensive treaty with the Soviets. No one had seen the Nazi war machine in action yet and the Poles thought they’d rather go it alone with only British and French promises.