One is that the other world leaders he is dealing with will still be grown-ups. The other is that the real US government -- the tens of thousands of senior civil servants and military officers who actually make the machine work -- are people with a lot of real-life experience, and they instinctively resist extreme policies and grand visions.
Even Trump's most radical ideas, like threatening to end America's 45-year-old "One China" policy -- and, implicitly, to recognise the independence of Taiwan -- will only destabilise the international order if other national leaders are panicked by his demands. In most cases, they will not be.
None of this guarantees Trump will not blunder into a big international crisis or a major war during his term, but the chances of his doing so are relatively low -- maybe as low as one in 10.
As for the "Manchurian Candidate" nonsense: Trump may have had significant Russian help during his election campaign, but he is almost certainly not an "agent of influence" for Moscow. The report by a British ex-spy that is causing such a fuss is actually too detailed: senior Russian officials do not give that much away to each other, let alone to Western spies.
Many people will be very frightened about the future when Trump swears the oath of office. The economic damage may be very bad, but the risk of war, even with China, is probably lower than they fear.
Back in 1976, when the Quebec separatists won an election for the first time, English-Canadians were terrified, and the anglophone minority in Quebec saw it as the apocalypse. It was only six years, after all, since dramatic terrorist attacks in Quebec by a different brand of separatists. But cartoonist Aislin (Terry Mosher) in the Montreal Gazette had the right idea.
He showed a close-up of separatist leader René Lévesque smoking his usual cigarette and telling the entire country: "OK, everybody take a Valium." It was better advice than even he knew: Quebec never left and the heavens never fell.
Gwynne Dyer is an independent journalist whose articles are published in 45 countries