@Mis -- Like many people, I believed the polls, which accurately predicted HRC's level of support but substantially underestimated Trump's. I didn't have any special insight.
But implementing policy is a different kettle of fish than telling people what they want to hear. For example, let's say Trump makes a policy proposal designed to severely limit illegal immigration and reduce the number of illegal immigrants already in the United States (but not via amnesty).
There are entrenched economic interests in the United States which LIKE having illegal immigrants as a cheap disposable low-worker-rights pool of labor. What if Trump gets in a room with representatives from Big Agra, Big Construction, Big Hospitality, Big Hospital, etc. who tell him, "You can't do that. Our labor costs will skyrocket. If you do that, we will support pro-immigration candidates in the 2018 midterm elections?"
What does Trump do then? His history is not one of being a negotiator and a compromiser. He may try to force his policy through, and he may succeed, but there will be insitutional resistance.
Or take, for example, his idea to seize outgoing monetary remittances from people in the US to Mexico as a way of trying to force Mexico to pay for his proverbial wall. It is not clear if those seizures are legal. If they are legal, they are a substantial portion of the economy of Mexico. Interrupting them would increase economic instability in Mexico, with probable secondary consequences in the global financial markets. Once again, the Powers That Be will probably meet with Trump and explain that they are not up for economic instability in Mexico and increased volatility in international financial markets. Will Trump fold? I don't know. And what happens if he does fold and has to tell Americans, "Sorry, I know I promised Mexico would pay for the wall, but your tax dollars are going to do it instead." It's not clear how that scenario will unfold, although the scenario is likely to come up.
OldSchoolTheSKOSlives 