If you watch the stock market's daily movements, 2014 has been an extremely bumpy year for stocks. The S&P 500 (^GSPC 0.12%) started out the year dropping nearly 6% on fears that the five-year bull market had come to an end. Yet now in less than two weeks, the S&P is back with about half a percentage point of a brand-new all-time record high. Investors are left wondering what's driving the volatility and why such a disparate set of individual stocks has led the index higher.

Akamai Technologies (AKAM -1.71%) has been the biggest winner in the S&P 500 since it bottomed out on Feb. 3, jumping more than 30%. The content-delivery network dodged a bullet when fears that its biggest customer would abandon it to build its own in-house offering proved unfounded, with Akamai instead renewing a contract to extend their relationship further. Given the importance of the Internet, Akamai's acceleration technology should remain relevant for a long time.

But companies from vastly different industries have also put in huge performances. Luxury retailer Michael Kors (CPRI -0.55%) has been a huge success ever since it went public, and it has redefined the pecking order in the luxury world, putting competitors to shame even as it produces almost unbelievably high growth rates in earnings and same-store sales. The stock's 28% gains show that high-end consumers are still strong and spending on what they perceive as the best-quality goods in the market.

For online travel review and booking service TripAdvisor (TRIP -3.16%), gains of almost 24% came largely from signs of consistent growth in its most recent earnings report, with total traffic climbing 50% and the site seeing better performance from click and display advertising as well as subscription revenue. By combining reviews with the ability to book travel, TripAdvisor hopes to give its customers the best of both worlds while remaining unbiased in its information.

Cliffs Natural Resources (CLF -0.91%) is the big surprise on the list, rising almost 23%. Even though the iron-ore and metallurgical-coal producer continues to face tough conditions in its industry, it has done a surprisingly good job at fending off hedge fund activists at Casablanca Capital. Part of the gains might have come from its stubborn resilience in the face of massive short-selling activity, with about 36% of its float sold short -- the most of any stock in the S&P 500. If Cliffs can survive through the worst of conditions in the steel industry, which uses its products as raw materials, then these gains could be the tip of the iceberg for Cliffs.

Look for a record test
One thing is certain: The S&P 500 is at a key inflection point. If it can indeed set new records, then investors might well gain enough momentum to start another leg of the long bull market. But if the S&P 500 falls short, then the disappointment could spur an even larger correction than we saw in January. Only time will tell which scenario plays out, but investors should be ready for both possibilities.