Trump has been roundly criticized for his handling of the Helsinki Summit. He met Putin without going though the process that normally accompanies such a high-level diplomatic meeting - the prior talks between lower level officials to clarify an agenda, to negotiate and establish goals that both sides could reasonably expect to announce with satisfaction to their citizens. That didn't happen, at least on the US side (one assumes it probably did in the Kremlin). Now the summit has concluded, many in the our government don't know what went on, and what was agreed to. Keeping secrets from his own top level officials, people Trump appointed is remarkable for its lack of transparency. How might Trump's choice to take this highly unconventional approach be explained?
The answer, I think is autonomy and accountability (or rather lack thereof). By not setting out goals in advance, Trump feels he could frame any outcome, whatever it might be, as a negotiating triumph. That gives him enormous negotiating freedom and autonomy. Engaging in a formal process in which others help set the agenda reduces his his negotiating autonomy. Not being clear about what he wants to accomplish and not being transparent about what is said means he can't be held accountable. No one can point to goals not achieved, since neither the goals not the outcomes are stated.
This approach, maximizing autonomy and minimizing accountability, might have suited a one-person business, whether that was his real estate dealing or his reality TV show, but is poorly suited to international relations. A failure in either of Trumps two prior careers, such as a badly negotiated sale or a drop in ratings, would have been disappointing for him personally, but would not have had mattered much for anyone outside his family. In negotiating with Russia, failure affects everyone in the US and to some degree has implications for every person on the planet. That's why his outlandish behavior is worrisome.