Trainee pilots, during that phase of training known as pilotage, are taught to navigate by ground reference. The danger is the students will assume things: The river, the golf course or any other landmark they see may not be the one near the destination. Assumptions are dangerous. My flight instructor warned me years ago, “Assumptions will kill you.”

But assumptions control everything, from the expectation your car will start in the morning to the belief this or that party will govern better.

In their turn, political leaders are governed by their own world of assumptions; assumptions that morph into beliefs and that, in turn, become in their proprietors’ minds facts and, in turn, policies.

Here are six of the motivating assumptions that underlie the presidency of Donald Trump to this point. They are flawed in different ways.

First: There is a huge unemployment problem. There isn’t. There is a shortage of workers, which is beginning to affect productivity in everything from home building to infrastructure construction.

If Trump is able to find a lot of new money for new infrastructure building and refurbishment, this skilled labor shortage will get worse. If you are a carpenter, crane operator, dump truck driver, electrician, plumber or welder, there is work aplenty. Just ask the electric utility industry or those building pipelines. The “help wanted” signs are out.

One caveat: The absolutely unskilled are close to being absolutely unemployable.

Second: The infrastructure is in deplorable shape and needs immediate attention. Here, the president is right. The question is, how will he fix it? In short, who will pay?

While the relevant committees of Congress have worked on the problem for years, they have been stymied by the lack of discretionary money in the budget. Every year, the highway bill makes it through with less money than its sponsors know it needs. Ditto state spending.

Public-private funding, part of the presidential mantra, is tricky and only applies in certain circumstances where, eventually, the private investor can get the money out and make a profit. There is no magic formula. Sorry.

Third: Illegal immigrants are prone to committing crime. The evidence is not there, and study after study shows the opposite. This belief erroneously feeds the widespread animus against immigrants, legal and illegal.

Fourth: The economy is a “disaster.” It isn’t and it wasn’t when the president was elected. There is growth, but it is modest.

Fifth: The United States can unilaterally banish radical Islam the from the face of the earth. Religions and their extremes are, at best, contained, not vanquished. Time and fatigue will put the evil genie back in the bottle, not American might.

Religions love martyrs — and Islam more so than most. Martyrdom is the sustaining force of today’s Islamic terrorism. Minting more martyrs will be counterproductive.

Sixth: Regulation has the United States trussed up and bound: a great giant cannot get up and produce goods and services and well-being for the people. Trump says that regulations should be reduced by two-thirds. But our regulatory burden is not as heavy as, say, that in Europe, and regulations do protect the public health and safety. That is why they were enacted in the first place.

Corporations complain and some regulations may be onerous. I have personally experienced the good and the bad. Two examples: when I was publishing magazines and I wanted them displayed on the streets of New York City, I had to offer the same incentives to 95,000 other newsstands where I had no readers. On the other hand, disposing of solvent used in a small printing plant was bothersome and slightly expensive but necessary. Without the EPA goad, the solvent would go into the sewers, with cumulative bad environmental and public health effects.

Bad assumptions make bad policy. Bad assumptions mostly come from hearsay and it would seem the president hears things from his friends: the time-honored New York City practice of schmoozing. It is a great tradition, but can lead to dubious assumptions, ergo beliefs and policies.