Nuclear North Korea

I have heard people comment that the North Koreans can’t believe that having one nuclear weapon, or even several, would mean that much.  “Don’t they know how many we have?  We would just nuke them out of existence!  They must be  ___________ (crazy, kidding, bluffing, doing this to fool their people, pick one).”North Korea has only the one wild card.  We don’t know what they think it’s worth.  It’s what they think it’s worth, that counts.  Our opinion is of no significance.
Having said that and written it previously at another blog site, I have an added reflection.  I have read (and heard in a briefing) that the US dropped more HE (high explosive) bombs on NK during the Korean war than were dropped on Germany in WW II.  While that seems unlikely to me, I have also heard that their subway tunnels are more than 100 meters below the surface and public bomb shelters are deeper still.  They are understandably concerned about being bombed and we never ruled out the use of nuclear weapons, in the event of a resurrgence of the Korean conflict.
Could it be that the NK leadership now thinks of things like they were in the Cold War, with Russia?  Since they also have one or more nuclear weapons, perhaps they feel safer and feel we won’t just attack them.  Unfortunately, that may increase the rhetoric and the tendency to make gambles on our behavior.