This report is from today's CNBC Daily Open, our international markets newsletter. CNBC Daily Open brings investors up to speed on everything they need to know, no matter where they are. Like what you see? You can subscribe here.

What you need to know today

Nvidia sinks
Nvidia shares plummeted 9.5% Tuesday, erasing nearly $300 billion from its market capitalization. Other chipmakers were affected too: The VanEck Semiconductor ETF sank 7.5%. Nvidia's slide continued in extended training, falling 2% after it was reported the company received subpoenas as part of an antitrust investigation.

Hammer's not that hot
The Institute for Supply Management monthly survey showed just 47.2% of purchasing managers reported expansion for August. That means the U.S. manufacturing sector is contracting overall. While the 47.2% figure is an improvement over July's, it's still lower than the expected 47.9%, renewing concerns the U.S. economy's slowing.

Ugly markets
Dragged down by Nvidia's plunge and weak economic data, U.S. stocks had their worst day since Aug. 5's sell-off. European stocks dropped Tuesday, with all major bourses and most sectors in the red, though food and beverage stocks managed to eke out a gain of 0.09%.

Low heat
U.S. crude oil futures fell more than 4% Tuesday to settle at $70.34 a barrel, more than erasing its gains for 2024. Oil's weak showing is primarily because OPEC+ intends to increase oil production, according to Reuters, and exacerbated by continued weakness in China's economy, which dampens demand for oil.

[PRO] Go for gold
When interest rates are high, gold prices tend to suffer — it's not as attractive as other options because it does not generate interest. On the other hand, when geopolitics run hot, gold serves as a good hedge against financial risks. Now with a rate cut on the horizon and tensions remaining high, Goldman Sachs is telling clients to "go for gold."

The bottom line

Some investing advice from an unlikely source: the recently reunited British band Oasis. In one of their songs, they croon, "Hold on/ Don't be scared/ You'll never change what's been and gone."

Investors should keep that in mind as they absorb the market's Tuesday move. The S&P 500 slipped 2.12%, the Dow Jones Industrial Average dropped 1.51% and the Nasdaq Composite lost 3.26% (ouch).

A confluence of factors was probably behind markets' weakness on Tuesday.

First, U.S. manufacturing activity remained in contraction territory for August. That resurrected concerns the U.S. economy isn't as strong as it looks.

Next, Nvidia sank almost 10%. Other chipmakers were hit by the shockwave as well. Intel lost 8.8%, AMD fell 7.8% and Qualcomm declined 6.88%. And in extended trading, Nvidia slipped around 2% on reports the U.S. Department of Justice is starting to investigate the chipmaker for antitrust reasons.

Last, some of that grim mood could have just been expectations.

Historically speaking, September has been the worst month for the S&P. The index's lost an average of 2.3% over the past 10 Septembers, according to FactSet data.

That's all to say: Yes, there are real reasons to feel concerned for the month. Fundstrat co-founder Tom Lee warned investors to be cautious for the next eight weeks, and thinks stocks could pull back by 7% to 10%.

But it's also important not to react impulsively.

Even though the ISM reading shows manufacturing activity declined, it's more than 42.5%, which generally signals expansion across the broader economy, noted Timothy Fiore, chair of the ISM Manufacturing Business Survey Committee.

And Nvidia's still up 118% for the year, even after its $300 billion wipeout in capitalization on Tuesday.

As another Oasis song exhorts, when it comes to investing for the long term, we should remember "The Importance of Being Idle." Don't let panic take over.

– CNBC's Jeff Cox, Alex Harring and Fred Imbert contributed to this report.