What happened 

Shares of The Trade Desk (TTD 3.35%), an advertising platform company, were plunging today after an analyst at Jefferies downgraded the company's stock and lowered his price target for its shares. 

The tech stock was down by 7.8% as of 1:32 p.m. ET. 

So what 

Jefferies analyst James Heaney downgraded The Trade Desk to a hold rating, down from his previous buy rating today. Heaney also lowered his price target for the company's stock to $55, down from $65. 

The analyst believes that investors have become "overly optimistic" about digital advertising and doesn't believe the market will grow as quickly over the next couple of years as some investors expect.

Heaney said that The Trade Desk has a "rich" valuation right now, though he also added that the company has "best-in-class" fundamentals. 

Now what 

Today's downgrade came at a particularly bad time, as investors were also processing the latest news that the Federal Reserve hiked interest rates by 50 basis points yesterday. 

The Fed also said that it expects to continue raising rates through 2023 until it reaches a final peak rate of 5.1%, which is higher than investors were expecting. 

Additionally, new retail data released today showed that retail sales fell by 0.6% in November, more than the 0.3% economists were expecting. 

It's understandable why investors would be nervous about The Trade Desk today, but they should also keep in mind that one analyst's opinion doesn't mean the company is doomed. 

Also, long-term investors should consider their original investment thesis before selling a stock to avoid making a decision based on what the investing crowd is doing.