You may not be surprised that Donald Trump hasn’t kept a number of promises as president, but you should be.

It’s a truism that politicians make promises they don’t intend to keep, but decades of academic research has actually shown the opposite: that presidents try to keep an average of about two-thirds of their campaign pledges.

That’s not exactly the case in the current administration, however. In several notable cases, President Trump has either directly broken a promise — such as his vow to release his tax returns — or simply not taken action on an idea — such as his pledge to enact term limits on members of Congress.

To be fair, it’s only Trump’s first year in office, and he still has time to follow through on some of his promises. But he’s also had a Republican-controlled Congress and could have taken action personally or through executive order on some of these pledges.

PolitiFact, a fact-checking website, has tracked Trump’s promises since his campaign began. Out of 102 promises on its Trump-o-Meter scorecard, 33 are currently stalled and seven broken, while only nine have been kept and seven ended with a compromise. Almost half — 46 — are considered in the works, but those include some hard-to-achieve targets like achieving energy independence and reversing China’s entry into the World Trade Organization.

By comparison, over eight years, the same scorecard ranked President Obama as having kept 258 promises, compromised on 146 and broke 129 — meaning he kept or compromised on three-fourths of his promises.

There are a couple reasons Trump’s having trouble keeping promises. Read below or watch the video above to learn more.

He’s not a career politician

First, as Trump liked to remind voters, he’s not a career politician. On the campaign trail, that meant Trump often made overly broad promises that riled up the audience in front of him that more experienced candidates tend to avoid.

That was the case with one of Trump’s biggest promises: to make Mexico pay for a border wall. There’s actually no simple way to force a foreign government to give the U.S. money, especially for a proposal which is unpopular among its own voters, and the Trump Administration already admitted as much when it asked Congress for $18 billion to start building the wall.

Trump maintains that Mexico will pay for the wall, somehow, but this will likely end up as a promise broken when he leaves office.

He’s a dealmaker

Trump also likes to argue that he’s a deal-maker, citing his long experience in New York real estate. But, again, that experience has cut against him in the world of politics.

As anyone who’s ever bought a home knows, real estate deals are all about getting to yes. When Trump is negotiating, he has a tendency to agree with everyone in the room in order to move closer to a deal, even though he may not end up seriously pursuing those ideas.

That happened during a meeting with Democrats about immigration.

Democratic Sen. Dianne Feinstein asked Trump if he would support a so-called “clean DACA bill” that simply protected undocumented immigrants brought to the U.S. as children. Trump responded that he would have “no problem” with that, but the White House later walked that back, since the GOP position was that a DACA fix had to be tied to border security.

He won’t rule anything out

Beyond his approach to deal-making, Trump appears to have a deep personal aversion to ruling any idea out. That means he ends up sounding like he’s endorsing proposals that are pretty unlikely to happen.

During an interview on the campaign trail, Trump was asked if he would build a database that tracks Muslims in the United States.

“Oh I would certainly implement that. Absolutely,” he replied.

The White House later claimed that Trump had never advocated for “any registry or system that tracks individuals based on their religion,” and neither the campaign nor the Trump Administration ever followed through on the idea of a Muslim registry, which would clearly raise serious constitutional issues. (The U.S. Census doesn’t even ask about religion.)

Most politicians would dodge a question like this by noting that was not something they were proposing, but Trump repeatedly refuses to rule out even the most unlikely ideas.

He uses empty threats to win the news cycle

Apart from real estate, Trump also has a background in New York City’s tabloid-powered news scene. Whether it was arguing for a building project or promoting his social standing, that’s led him over the years to make more than his fair share of empty threats and promises.

On the campaign trail, that most notably played out when he called the 18 women who accused him of sexual misconduct “liars” and pledged to sue all of them after the election.

In reality, he never sued, and after one of the women sued him, his lawyers argued that as president he was too busy and important to face the lawsuit, but the threat helped him rebut the accusations in the moment.

He’s just the president

Finally, Trump has trouble keeping some of his promises for the same reason as his predecessors: He’s only the president.

Though candidates — and voters — sometimes forget it, the president has no real authority to force Congress to take action on a specific issue, other than to issue broad veto threats and barnstorm for his proposals.

That means Trump can end up failing to live up to a promise to eliminate the carried interest loophole or reduce the number of tax brackets to just three or create targeted child care tax credits because Congress doesn’t pass a bill he can sign to make them law.

Again, that’s one reason why career politicians avoid making these promises in the first place. Trump won the Republican primary and the general election in large part because he was willing to say things other politicians weren’t, whether that was because of his background, his personality or his campaign strategy.

But now that he’s president, he’s learning the hard way how hard it is to keep those promises.

Get our Politics Newsletter. The headlines out of Washington never seem to slow. Subscribe to The D.C. Brief to make sense of what matters most. Please enter a valid email address. Sign Up Now Check the box if you do not wish to receive promotional offers via email from TIME. You can unsubscribe at any time. By signing up you are agreeing to our Terms of Use and Privacy Policy . This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply. Thank you! For your security, we've sent a confirmation email to the address you entered. Click the link to confirm your subscription and begin receiving our newsletters. If you don't get the confirmation within 10 minutes, please check your spam folder.

Contact us at letters@time.com.