For one thing, people believed that "the bomber would always get through". Given their situation - surprised and under furious attack on land - one could hardly expect the Dutch to stop it, but as it turns out Fighter Command begged to differ.
For another, people did hugely overestimate the damage it would cause. No consolation to the dead, I know, but the British government set up emergency measures on the premise that bombing was going to be an absolute slaughter.
For another, everybody expecting bombers to have a shattering effect on morale. Once again, look at the specific Dutch situation: surprised and getting the worst of a land battle. They decided to end the seemingly hopeless resistance before any more civilian destruction. But in Britain, it was seen that a mobilised and prepared country could quite literally shrug and carry on when it came to morale.
So, these assumptions all work against the Czechs: it was thought that everything would be blown to smithereens and morale would break down. The lesson seems to me to be that if for some reason the Czechs had decided to mount what they knew was a hopeless resistance, people would die and heritage and industry would be destroyed, but life would carry on, factories would run, and fighting would continue at the front. This was not something people took for granted before the war.