On Friday, the S&P 500 (^GSPC 0.13%) fell almost 1%, bringing its total drop for the week to more than 2.5% and raising calls of a potential correction. Yet amid the near panic that investors saw at certain points during the week, some of the stocks that ended up in the losing column this week were surprising. Let's look at Delta Air Lines (DAL -1.38%), AbbVie (ABBV -0.11%), and SanDisk (NASDAQ: SNDK) to see what they lost so much ground this week and whether it's justified.

Delta Air Lines fell 6% this week, as investors prepare for what's likely to be a poor winter quarter because of weather problems. But Delta has a long history of outperformance during the current market cycle, with the airline having much more flexibility than its rivals in how to deploy its ample free cash flow toward bettering its business or rewarding shareholders. With its role in pioneering ancillary charges like baggage fees while also keeping capital expenditures down, Delta Air Lines could keep soaring far into the future even when the airline industry doesn't enjoy as many advantages as it does right now.

AbbVie dropped more than 10% in the general exodus from health-care and biotech stocks. But the thing to remember about AbbVie is that it hasn't soared nearly as much as higher-profile biotech growth giants, largely due to uncertainties about how AbbVie will transition away from its heavy reliance on sales of blockbuster drug Humira when it loses patent protection. Still, AbbVie actually had good news this week, with positive late-stage study results having competitive implications in the hot hepatitis C treatment market. With Humira going off-patent in 2016, AbbVie needs to act fast, but it has the ability to find winning therapies and bounce back from its patent-cliff issues.

Source: SanDisk.

SanDisk declined 9%. Investors got nervous about memory-chip makers this week, as the group had enjoyed some powerful gains over the past year and looked poised for a pullback. But SanDisk is in a powerful position in the industry, with its flash memory helping to power electronic devices of all kinds, ranging from smartphones and tablets to portable cameras and camcorders. More importantly, SanDisk has made an impressive foray into solid-state drives, both in high-end drives with pure solid-state memory as well as through partnerships with one hard-disk drive giant to produce solid-state hybrid drives that bridge the price and performance gap between old-style hard-disk drives and more expensive pure solid-state drives. Even if margins for memory decline, SanDisk has room to enjoy long-term growth as emerging markets catch up to developed markets and their hunger for faster storage.

Just because stocks drop doesn't mean that they're bad investments. In fact, many times, a drop is exactly what you need to give you the right risk-reward trade-off to buy a stock.