The S&P 500 Index (^GSPC -0.88%) fell 0.15% on Thursday, the third straight day stocks closed lower. This comes on the heels of a solid two-week period that saw the index gain almost 5% ahead of earnings season.

This week, a steady diet of mixed results and uncertain outlooks about the economy has investors reversing course. Executives have been very muted when talking about the near-term outlook; rising cases of the coronavirus, along with congressional gridlock over additional economic stimulus, have investors on the fence. 

Shares of Vertex Pharmaceuticals (VRTX 0.20%) fell sharply today, losing nearly 20% after the company reportedly pulled the plug on a drug in clinical trials. The stock of United Airlines (UAA 1.81%) fell 4% after the carrier announced a brutal third quarter.

On the upside, oil producer Apache's (APA 0.56%) shares gained 6% (tops in the index) after releasing some estimates for its third-quarter production that investors liked, while shares of Charles Schwab (SCHW 0.67%) and Walgreens Boots Alliance (WBA 3.69%) gained 5% after reporting earnings.

But beyond these specific, material catalysts, today's biggest movers weren't driven by anything specific. Actually, well over 300 of the stocks in the S&P 500 closed up on the day.

Red arrow pointing left, dozens of black arrows pointing right.

As goes big tech, so goes the market. Image source: Getty Images.

The biggest reason why the index closed lower today was the usual suspect: big tech.

Big tech wrecks today's rally

The tech sector fell about 0.5% on the day, led lower at the top. Facebook shares fell 1.9%, with AppleMicrosoft, Amazon, and Alphabet all closing lower. The massive size of these companies was more than enough to offset the gains at the other end of the index. 

Vertex's rare miss rattles investors

Shares of the biotech giant fell 21% today, following news that a potential treatment for a genetic condition was reportedly being discontinued. According to reports, Vertex's VX-814, which is in clinical trials, is being discontinued after some patients exhibited elevated liver enzymes. 

That's a pretty big beating for what was expected to be a moderately successful drug that would face a lot of competition. It's possible some investors mistook the shelving of VX-814 as a bad signal for another drug, VX-864, also in trials. Vertex said that the latter remains on track to produce some data early next year. 

United continues to burn through cash

Shares of the airline giant fell almost 5% today after the company released third-quarter results that showed just how brutal the coronavirus pandemic continues to be for airlines. In the third quarter, United reported it was burning $25 million per day as commercial air travel remains some 70% below last year's levels. A large portion of that cost was for employees, whom it had to keep on its payroll due to the terms of federal bailout funds provided to the industry. 

United is already starting to furlough workers to lower expenses, in order to preserve as much of the $19 billion in cash and available debt it can access. Meanwhile, it has also increased its cargo revenue (up about 50% from last year) to help offset costs while flying people isn't a viable option. 

Apache, Schwab, Walgreens surge after exceeding expectations

Oil producer Apache, online broker and investment manager Schwab, and pharmacy giant Walgreens Boots Alliance shares were tops in the index today, putting on a master class of beating low expectations.

Apache didn't report earnings, but it did announce a range of metrics, including average realized oil and natural gas prices, and some costs, to "further assist analysts with their third-quarter earnings models." In short, those numbers were good enough to get investors hopeful that the independent oil and natural gas producer was able to make the most of the modest uptick in oil demand and prices we saw during the summer months, when demand is highest on a seasonal basis.

Investors won't know exactly how this worked out on the bottom line for another three weeks; Apache said it will report on Nov. 5. And a bigger concern: Oil demand and prices have both slipped recently. Coronavirus cases climb and oil giants Russia and Saudi Arabia prepare to take action to grab market share when demand does recover. The oil industry isn't out of the woods yet. 

Schwab did release its third-quarter results today, and like Apache, the company was able to make the most of low expectations. Net income and revenue both came in double-digits below last year's quarter, but since investors were expecting even worse results, the reception was positive. 

For Walgreens, the story was a combination of results that both beat expectations and were pretty solid, along with investors being willing to use their imaginations and think about the results trending better next year. Shares are still down more than 30% this year, so patient investors willing to ride things out might buy this Dividend Aristocrat now, and count on at least getting a steady dividend while they wait for things to get better.