Arista Networks (ANET) reported first-quarter results that beat analyst estimates on both the top and bottom lines. Revenue came in at $2.71 billion, up 35% from a year ago and ahead of the $2.61 billion consensus. Earnings per share of $0.87 also topped the $0.81 estimate.

So why is the stock down 13% in after-hours trading?

Because sometimes, even a beat isn't enough. Investors, it seems, were expecting an even bigger number — and when they didn't get it, they sold first and asked questions later.

CEO Jayshree Ullal struck an optimistic tone, saying, "Arista is off to a strong start in Q1 2026, with both our results and our industry-leading net promoter score. We are uniquely positioned to deliver the mission-critical confluence of secure client-to-campus-to-cloud and AI networking."

The company also highlighted new products aimed at the AI data center boom, including XPO high-density liquid-cooled pluggable optics that it says can reduce networking racks by up to 75% and save 44% of floor space. Arista also introduced a universal AI spine to help power AI centers.

Looking ahead, Arista guided for second-quarter revenue of $2.8 billion, above the $2.77 billion consensus, and adjusted EPS of $0.88, versus the $0.85 estimate. Again, a beat — but apparently not enough of one to satisfy the market's lofty expectations.

The stock, which had traded in a 52-week range of $82.80 to $179.80, fell to $146.65 in after-hours trading. The sell-off is a reminder that in a market already pricing in perfection, even good news can feel like bad news.