Now, where the Poles may have goofed, and I say this is one who is very sympathetic to the Poles, is their insistance that Soviet troops not be based in Poland, as the British and French wanted, so as to conclude an alliance with Russia against Hitler.
In hindsight, considering that the Soviets got their half of Poland anyway, through the Non-Aggression Pact, it may have stopped Hitler from invading Poland.
Memories of 1920 were too fresh in Polish minds.
And remember, when then Soviets did enter Poland, the second time, it took almost 50 years to get rid of them.