The problem is that for Ukrainians the threat has been near constant since 2014, 8 years now. So people have heard the "news" thousand times before that invasion could happen any day now, and it did not happen... Until today.
Like, I get that the previous buildups could be dismissed as saber rattling and training exercises, but Putin literally announcing, "HEY I'M COMING IN, I'M SENDING IN TROOPS TO UKRAINE NOW", how do you dismiss that?
You're never sure whether the Chinese submarine is "exercising its rights to international waters" or is preparing for a strike; or the US-Swedish troops are just making friends with each other or getting ready to invade.
That's totally apart from the obvious "sabre rattling" bit.
Kind of like the IT admin that doesn't check backup integrity often enough because there's never been a data loss issue in years.