Folks are coming back to McDonald's (NYSE:MCD), and that's getting Wall Street excited. Shares of the world's largest burger chain hit a new all-time high on Monday, after Mickey D's posted encouraging sales results for the holiday quarter.

However, for every check, there's a reality check, and in this particular case, there are a few things to keep in mind when digesting the 5.7% year-over-year spike in comps for the chain's domestic restaurants.

Global comps rose by an encouraging 5% for the quarter, but the real reason for the market going McGiddy about McDonald's is the welcome improvement in stateside locations. Let's take a look at three reasons this isn't amazing news.

1. Unit-level sales still need to improve
McDonald's had been posting negative comps for its U.S. stores since the summer of 2013 until the third quarter of 2015, when it clocked in with a 0.9% year-over-year advance. A 5.7% spike is impressive, but keep in mind that the streak of negative comps means this figure is sandbagged by declining comps during the holiday quarters of 2012, 2013, and 2014. 

Comps declined 1.4% during the final quarter of 2013, followed by a 1.7% slide a year later. That means the 5.7% increase this time around is just a 2.4% improvement over three years. Are we really applauding improvement at an annualized clip of 0.8% over the past three years? That isn't even keeping up with inflation.

2. Breakfast is a game-changer, but only if you're playing the short game
McDonald's credits the bounce to mild weather and the decision in October to start serving many popular breakfast items all day long. The weather is always going to be unpredictable, but let's take a closer look at the Sausage McMuffin you had for lunch.

Expanding breakfast was a no-brainer. I wasn't the only one arguing that it would be the perfect tonic to turn negative store-level trends around. However, we can't assume this will lead to heartier gains over time. It could just be a novelty, with folks going out of their way to fork into hotcakes for dinner because it's suddenly available. We still don't have a good read on customer satisfaction. Is broadening the lunch and dinner menu slowing down the drive-thru lanes and in-store lines?

Even if it's not a novelty, the party will be good only through the next three quarters. Once the fourth quarter of 2016 rolls around, we'll be comparing things on an apples to apples -- or oatmeal to oatmeal -- basis.   

3. McDonald's stock was strong even when financials were weak
It's been widely known that McDonald's was struggling from the summer of 2013 through the summer of 2015. However, nobody seemed to be telling investors what was going on at the store level.

Shares of McDonald's were trading higher on a dividend-adjusted basis on July 23, 2015 -- the day it posted its eighth consecutive quarter of negative stateside comps -- than they were two years earlier, when it had posted its last positive report. 

The stock was never really out of favor. The stock's established brand and chunky yield kept the declines in check, and those gains have only been padded in recent months. McDonald's stock rose in each of the last four quarters of 2015, and it's bucking the trend so far in 2016 by trading higher again in January. Investors should be encouraged by the rebound in McDonald's fundamentals, but those holding out for a lot more upside may want to consider that those gains already materialized in the months leading up to Monday morning's results. 

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.