"Unpredictability" is the key to understanding President Trump's negotiating plan as he heads into his roll-the-dice summit with North Korea's Kim Jong-un.

What we're hearing: Trump loves to say that every other U.S. president was predictable. He believes foreign affairs has always been overly scripted and his predecessors were "totally predictable," which let their adversaries run rings around them.

A source who recently spoke to Trump about his upcoming meeting with Kim Jong-un paraphrased the president's private monologue:

"No one knows what I'm going to do. They are over there trying right now to analyze every statement I'm putting out to get a sense of what's going to happen when I walk into the room. But the fact of the matter is nobody knows."

Trump loves to watch the media try to predict what he's going to do and say about any number of things, including North Korea, and he gleefully tells aides: "They have no idea."

“Kim Jong-un’s entire lineage is having people think he might be crazy. Trump’s like: 'You’re crazy? How about this?'” a source said a while back, during the phase of Trump calling Kim "Little Rocket Man" and taunting him by saying he has a bigger nuclear button.

One of the biggest challenges: How will Trump ever know he's struck a good deal after the photo op and North Korea's initially dramatic destruction of some of its nuclear facilities?