Although most consumers have yet to buy their Halloween candy, forecasts for holiday sales are already rolling in. The National Retail Federation, or NRF, just released its estimate for spending for Holiday 2017 (the months November and December) on October 3.

“Our forecast reflects the very realistic steady momentum of the economy and overall strength of the industry,” NRF President and CEO Matthew Shay said. “Although this year hasn’t been perfect, especially with the recent devastating hurricanes, we believe that a longer shopping season and strong consumer confidence will deliver retailers a strong holiday season.”

Its forecast of a 4% increase in dollars spent reflects healthy economic growth in the U.S. A holiday shopping season that begins one day earlier and includes five full weekend days of shopping versus last year provides an extra boost.

While one extra day of shopping may seem inconsequential, an additional 24 hours of frenzied consumer spending can make or break a holiday season. Add to that the psychological boost of a full weekend of shopping before a Monday Christmas and retail might find some green in its stocking this year.

Holiday sales can make up as much as 20-40% of a retailer’s annual sales. Seeing that some retailers make all of their annual profits in the fourth quarter highlights how critical a successful holiday season can be for any retailer.

I think the NRF’s forecast seems reasonable but back-checked its prior years of data to see how closely actual spending matched the estimate that it assembles via interviews with over 2,000 consumers.

It turns out the NRF’s estimates skew to the high side but are generally in the ballpark of actual spending trends.

The devil, however, is in the details.

Despite overall holiday spending increasing 4% last year, a bit above the NRF’s 3.8% forecast, many retailers missed estimates for sales growth. Target (NYSE: TGT), Macy’s (NYSE: M) and Kohl’s (NYSE: KSS) all delivered lumps of coal to investors in early January with announcements of lackluster sales.

In unraveling the NRF’s data, it seems that online sales were the Grinch that stole brick and mortar sales. E-commerce or “non-store” sales leaped almost 13%, but store sales limped by with 2% growth.

This is not a new story. Everyday investors wake to another report detailing the triple-digit growth of e-commerce or another retail death caused by Amazon.

Despite the fact that Target, Macy’s and Kohl’s all saw significant growth in their online sales, the merciless price competition forged by instant and easy price comparisons, slashed sales and profits for many retailers.

Brick and mortar retailers have a huge nut to cover in the form of lease expense. The formidable expense of salespeople and the cost of running the store make every incremental sales dollar a crucial ingredient to delivering profits.

Of course, how well a company does this holiday season is built on its results from last year. Wall Street cares most of all about comparisons; not just what number is delivered but how it compares to last year’s number.

Fast forward to this holiday season, and I’ll be doing what many analysts seem to forget to do. I’ll be reviewing and dissecting exactly how each retailer did during last year’s holiday season and figuring out what the impetus was behind their success or failure.

Did a retailer succeed due to a spike in sales of a fad item or due to the demise of a competitor? That event is unlikely to be repeated, and that company might have trouble hitting its targets.

Did the retailer experience a logistical problem with product availability or delivering on time? If those issues are fixed, that company might just beat expectations.

I’ll be sharpening my pencil in an attempt to quantify the events that drove holiday 2016 results and the ensuing assumptions behind 2017 estimates.

At the end of the day, I should have two piles of retail stocks. Those I expect to deliver a lump of coal will result in a bearish bet, and those I expect to deliver good tidings will result in a bullish recommendation.

There’s no reason not to profit from both the Naughty and the Nice list this holiday season. At my Profit Catalyst Alert service, I endeavor to provide valuable bullish and bearish trade recommendations.