Wall Street finally had to deal with some disappointment on Wednesday, but even though major benchmarks eased back from their record highs, they still fared better than many investors had feared coming into the session this morning. Though they initially lost a substantial amount of ground, optimism about the general state of the U.S. economy helped pull key indexes back closer to the unchanged level. Yet despite modest declines for the market as a whole, some stocks saw much more severe pullbacks. Ambarella (AMBA -1.59%), Signet Jewelers (SIG -0.21%), and NetScout Systems (NTCT -3.10%) were among the worst performers on the day. Below, we'll look more closely at these stocks to tell you why they did so poorly.

Ambarella loses visibility

Shares of Ambarella fell 9% as investors considered second-order effects on the camera chip provider from weakness at one of its main customers. GoPro (GPRO -1.46%) said earlier this week that its fourth-quarter results would be far below expectations and it plans to stop selling drones. That's bad news for Ambarella, because even though it has done what it can to reduce its reliance on GoPro-related sales, GoPro was still responsible for more than a fifth of Ambarella's top line in the third quarter. Ambarella will have to move aggressively to replace lost drone business with new supply contracts in order to avoid a big disruption to its business.

Camera hardware and chip board to operate it.

Image source: Ambarella.

Signet sells less

Signet Jewelers stock dropped 7% after the jewelry retailer said that its holiday season revenue fell 3% on a 5.3% drop in same-store sales. Although the Zale division had solid gains and Signet managed to post double-digit percentage gains in e-commerce sales, Signet's ongoing efforts to outsource its credit services kept having negative impacts on its overall performance, especially at its Kay Jewelers unit. The jeweler also guided full-year fiscal 2018 earnings toward the lower portion of the range it had projected previously, although it also said that tax reform benefits would likely boost earnings by about $0.28 per share. Signet desperately needs to turn things around now that a streak of poor performance has taken hold.

NetScout warns investors

Finally, shares of NetScout Systems finished down nearly 14%. The business intelligence solutions specialist issued preliminary results for its fiscal third quarter, blaming sluggish capital spending trends across the industry and the substantial decline in business from one of its major customers for the shortfall. NetScout did say that it would do a stock repurchase of at least $250 million, which would represent more than 10% of its market capitalization. But investors didn't seem appeased by that move, and concerns about ongoing weakness in the industry could weigh down NetScout well into the future.