Shareholders of Chipotle Mexican Grill (NYSE:CMG) caught a break last week. The stock moved 15% higher on the week, rising as the stock market in general was selling off. 

It didn't seem as if it would work out that way when the week began. The stock dipped below $400 in intraday trading on Tuesday, the first time we've seen that happen since the summer of 2013. That was before the stock experienced back-to-back days of 6% gains on Wednesday and Thursday, following that up with a nearly 5% pop on Friday.

Last week's pop and the prior week's 14% slide find the stock essentially back to where it was when the year began, but it's not as if we can say that it's been marching in place.

We know why the stock got clobbered during the first trading week of 2016. The toll of the widely publicized norovirus and E.coli outbreaks proved to be too much to its once-sterling reputation. The "food with integrity" company announced on Jan. 6 that comps for the holiday quarter would decline 14.6% since the prior year, a sharp downward revision from its warning a month earlier that comparable-restaurant sales would clock in with a decrease of 8% to 11%. 

We also know why the stock got a boost last week. Chipotle had a highly anticipated presentation at the annual ICR Conference in Orlando last week, announcing there that it plans to shut down its restaurants for a few hours on Feb. 8 for an all-staff meeting to cover food safety and changes to its operating procedures. 

The market's swinging high and low here, but investors need to sift through the volatility. The big drop two weeks ago and the big pop last week were overreactions. 

No one should've been surprised by Chipotle's abysmal quarter. It was on Dec. 4 that it guided the market to brace for an 8% to 11% dip in comps, but it was clear that Chipotle's problems were mounting as the quarter came to a close. Besides, as brutal as a 14.6% plunge in comps for a company that has done nothing but post positive results as a public company, it is being pitted against a 16.1% surge a year earlier and a 9.3% spike the holiday quarter before that. 

There's also not a lot to get excited about last week's development. Closing all of its restaurants until 3 p.m. local time on Feb. 8 is mostly lip service. It doesn't have to do that to get its message across, and given the high employee turnover in the dining industry, it won't be long before your burrito is being rolled by an assembly line that wasn't there that day. 

Last week's pop was mostly a sigh of relief for a former market darling that had given up too much ground before that. It kicked off last week trading 46% lower than its all-time peak this past summer. The bounce was natural after the wave of selling, and it will take more than just an all-staff meeting to woo customers back. Things will be great for shareholders when patrons do come back, but just saying that you want to reduce the risk of another outbreak to "near zero" and missing out on a day's lunch traffic isn't going to be enough. It's the first step. There will have to be many more steps in the future.  

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.