"It ain't over 'til it's over," when it involves North Korea. It is worse when the unpredictability of Kim Jong Un is pitted against that of U.S. President Donald Trump. Thus it was entirely foreseeable that Trump's White House would issue a letter announcing that the summit planned for June 12 "will not take place."
First, there is a history of failures with the Koreas summits. Both the 2000 and 2007 Sunshine Policy efforts were aborted due to intransigence on several fronts.
Second, it was only in January that Kim threatened that his nuclear launch button was "always on the table." In response, Trump boasted that his nuclear button was "much bigger" and "more powerful" than Kim's. A move from hawkish outbursts to a complete turnaround in favor of negotiations was strong indication that yet another reversal from either of the leaders was possible. The two leaders' egos were also evident when each claimed playing a bigger role than the other in making the Koreas summit a reality.