Earlier quoted context omitted.
Are all overreactions sudden? Man A is pushing man B repeatedly and yelling at him as a bar dispute escalates. Man B pulls out a gun and shoots man A. Overreaction? Yes. Sudden? Not necessarily.
Man B push around man A, insult him, poke him. Man A ask him to stop. Man B pulls out a gun and shoots man A. Here, ftfy. Poland saw what what Germany did to Czechoslovaquia, decided that negotiations would only happen after a demilitarization and de-escalation. But it's true it wasn't sudden, poland was preparing for the war, the attack from both side (cooperation between Germany and Russia) is what took them by sur…
I was strictly illustrating a counter example to the implied notion that overreaction implies suddenness.
To further demonstrate that this is a misunderstanding on your part, it wouldn’t even make sense for me to have A and B correspond to the Germany/Poland situation - that would make my argument circular!
It isn’t very kind to take an interpretation that would set the speaker’s argument as circular, when an alternate and trivially-demonstrated-as-more-valid interpretation is also available. I believe the advice is often stated as - assume good intent.
On your second point - this is an elementary school tier interpretation of history. Poland itself did not have anywhere close to sufficient leverage to make such decisions about delaying negotiations. They were able to do so solely due to Britain’s backing their decision with force. Why did Britain back them? Why do you believe the history book written by the winners so easily on a topic so fuzzy as motive?