The tax preparers at H&R Block had to take a new class before their busy season started this year: empathy training. For real. They have added this training. H & R Block preparers listened to a mock exchange between an employee and a customer whose refund would not just shrink but disappear. The fictitious client had received a $1,500 refund last year, but this year would owe $575.

The playacting was a foreshadowing of what they knew was coming. The tax overhaul that took effect last year promised relief, but now that returns are being filed, some people are baffled. They’re getting smaller refunds — or sometimes having to write a check — even though nothing in their situation seems to have changed.

The average refund among early filers was down 8.4 percent, according to the Internal Revenue Service. The smaller checks, in some cases, stem from the loss of certain deductions. For others, it’s because less money is being withheld from their paychecks. The I.R.S., in trying to more closely match the amount held out of paychecks with the amount that taxpayers will owe, changed its withholding tables.

The result is that taxpayers may be paying less over all but still getting a bill after filing their return. That has caught many people off guard.

The overhaul has been President Trump’s signature accomplishment. It lowered tax rates for businesses and individuals, and it provided a break to self-employed people and those with so-called pass-through businesses, where income passes through the business to the owner’s personal tax returns.

But it also eliminated or cut back some popular deductions, most notably capping the deduction for state and local taxes at $10,000 — a provision that drew significant criticism from residents of high-tax states. Although most people will see their tax burden decline, the Government Accountability Office expected about four million people to pay more.