Fortune reported retail sales slid a worse-than-expected 0.3% in September, weakness that caught investors and retail observers off guard as some had hoped falling gasoline prices would boost spending on the wares retailers sell. Sales on a sequential basis were weaker for apparel, building material and garden equipment, automobiles and furniture and home furnishing items. One bright spot was for electronics, bolstered by the launch of Apple’s (AAPL) newest iPhones.

“Retail sales were surprisingly weak in September,” NRF Chief Economist Jack Kleinhenz said. “Despite increasing consumer confidence, an uptick in employment, lower gas prices, and with inflation in check, consumers still slowed spending.”

The disappointing data helped pushed U.S. stocks briefly to an eight-month low on Wednesday.

The retail price of gasoline for the average American has dropped nearly 15% since late June, according to The Wall Street Journal, which cited at a from Gasbuddy.com. That should have led to higher sales at retail stores, as gas prices are especially transparent to consumers that often pass dozens of fuel retailers as part of their daily commute. For example, a survey conducted last year by the National Association of Convenience Stores found that nearly nine in ten consumers say that gas prices impact their feelings on the economy.

But some observers say consumers don’t pay attention to gasoline prices as much as media reports indicate, especially those with a higher income (a group that spends more on discretionary goods).

“We all tend to overestimate the sensitivity of gasoline prices, both the upside and downside,” said John Canally, chief economic strategist for LPL Financial. “We all expect an immediate response that consumers with more change in their pocket to go out and buy stuff.”

Canally said the September retail data is at odds with other economic indicators, pointing out that employers continue to add jobs and the housing market is recovering. The deceleration in consumer spending is problematic as retailers gear up for the holiday season, and a few factors — such as warmer-than-usual weather and fears surrounding the Ebola epidemic — could also play a role in how people spend.

“The economy is two-thirds consumer, so if they throw in the towel, there is only so much that housing and capital spending can do,” Canally said. “The momentum heading into the fourth quarter isn’t so good.”

The poor retail sales for September shouldn’t have caught investors entirely off guard, as there were a few canaries in the coal mine that were sounding the alarm. J.C. Penney (JCP) earlier this month lowered its third-quarter comparable sales forecast after a disappointing September. Gap (GPS) Chief Executive Glenn Murphy last week said September “proved to be more challenging than we expected.”

Still, some are cheering the fact that less pain at the pump can help their consumers. At Wal-Mart’s (WMT) analyst day presentation on Wednesday, a marketing executive said lower fuel prices could be a “tailwind” this holiday season.

—Fortune’s Phil Wahba contributed to this report.