WASHINGTON - Steady hiring is supposed to fire up economic growth.

Cheap gasoline is supposed to power consumer spending.

Falling unemployment is supposed to boost wages.

Low mortgage rates are supposed to spur home buying.

America's economic might is supposed to benefit its workers.

Yet all those common assumptions about how an economy thrives appear to have broken down during the first three months of 2015.

The economic benefits that normally would flow after a full year of solid hiring have yet to emerge. Just 126,000 jobs were added in March, the government said Friday. Average weekly paychecks fell.

Restaurants cut back on hiring because savings at the gas pump didn't lead to more dinner reservations. Builders and manufacturers each cut 1,000 workers from payrolls, thanks to tepid construction activity and so-so factory orders.

Had Friday's report been released a few days earlier, "it would have been laughed at as a great April Fools' joke," said Gregory Daco, head of U.S. macroeconomics at Oxford Economics.

The middling gains confirm evidence elsewhere of a broad economic slowdown. During the first three months of the year, the Atlanta Federal Reserve forecasts that the economy actually came to a standstill - failing to grow at all.

Some of the first quarter's slowdown is no doubt due to an especially harsh winter. Yet nearly six years into the recovery from the Great Recession, the economy's muddled progress seems inescapable. A long-awaited breakout remains elusive, suggesting that the economy's direction has never been quite as simple as some analysts, politicians and bar stool philosophers would have it.

Now, some analysts are pointing to factors that might have been downplayed or overlooked this year. Others are holding to their projections about the economy as it theoretically should be. After all, they reason, March may prove to be a hiccup akin to what happened in 2014, when a first-quarter slump was followed by a burst of growth in the ensuing months.

Here are some factors that help explain why the U.S. economy isn't accelerating as you might expect.

- NASTY WEATHER

For parts of the United States, it felt like endless winter. The snowfall and frigid temperatures that lingered until the closing days of March can freeze economic growth.

Construction crews built fewer homes: On a seasonally adjusted basis, builders broke ground on 17 percent fewer homes between January and February. Shoppers skipped visits to the mall and auto dealers, choosing instead to crank up the thermostat. Retail sales fell in January and February.

If weather was a culprit, it might actually be an encouraging fact. It would mean that the economy remains fundamentally healthy - something that would become evident once the clouds lift and the sun emerges in spring.

- STRONG DOLLAR

Many U.S. factories ship their wares around the world. But because the U.S. economy has fared better than its trade partners, U.S. factories are now at a disadvantage: America's relative health has helped drive up the dollar's international value. Goods from U.S. factories are about 20 percent costlier in Europe than a year ago, an increase that has dampened sales.

So the U.S. economy's very strength has helped create a weakness.

Which is why Maryland-based Marlin Steel has held off on plans to hire more metal workers.

"It's not just me selling into Europe - it's all of my clients selling into Europe," said Drew Greenblatt, president of Marlin Steel. "They're all dealing with the pain."

- OIL'S SLICK MOVES

A barrel of crude oil costs under $50, having more than halved in price since June. This means wells are pumping out smaller profits, if not losses. When oil prices plunge and billions of dollars are at stake, oil companies tend to respond quickly to curb production. The number of active rigs has fallen 50 percent since October, according to Baker Hughes, the oilfield services company. This has led to layoffs, tighter budgets and fewer orders for equipment, all which hurt growth.

Consumers, by contrast, have yet to respond to their savings from cheaper gasoline by spending much more. The lag means that the oil companies' cutbacks have yet to be offset by greater retail spending. So the economy has suffered all the downside, while the upside has yet to appear, said Carl Tannenbaum, chief economist at Northern Trust.

Tannenbaum predicts that consumers will eventually respond to gas prices, which are on average 33 percent lower than a year ago. When they finally do, the economy should perk up.