its because healthy markets shrug bad news and continue in the direction and unhealthy markets don't and react viciously. Think of it tired market versus not tired, can overcome obstacles
NZD can be regarded as a sub-set of AUD. The two economies are closely linked, almost everything that NZ buys or sells goes through Australia. AU's population is 5x NZ's. If Australia and the AUD are doing well, be wary of shorting NZD.
Markets move because they have to (where the stops are). So times when the market doesn't move, it didn't have to. Simple as that. You might understand someday.