It seemed like a small thing when Hitler announced on March 16, 1935 that Germany would breach the terms of the Versailles settlement by bringing in conscription and training 100,000 men a year without dramatically expanding its military.
But when the former Allies did not react, he quickly announced a tripling of the armed forces in May (along with renaming it the Wehrmacht from the Reichswehr, already purged of Jews a year earlier), then remilitarized the Rhineland a year later while the French stood feebly by despite still having a far bigger army.
Then came the Czechoslovak crisis, Munich and… well, you know the rest.
Not every ominous deed foreshadows disaster if ignored, of course. But almost every disaster is foreshadowed by ominous deeds ignored. Like this one.