Does encouraging paranoia in others relieve your own somehow?
If North Korea was 100% ready, and tossed everything they have had and hit with 100% reliability, they could devastate a few U.S. citys downtown areas. That's several huge "ifs," but it's not completely implausible. Horrific, too.
The U.S. retaliation would wipe out their government entirely, with the rest of the nuclear-armed world cheering on.
So why on Earth would North Korea do such a thing? What would they gain?