It's August 2004. A 20-year-old Harvard dropout named Mark Zuckerberg is raising a small round for "TheFacebook," a social network that only a few hundred thousand college students can even access. You're being pitched as an angel investor.

It's February 11, 2000. Pets.com — backed by Amazon.com, fronted by a wildly popular sock-puppet mascot, fresh off a multimillion-dollar Super Bowl ad — has just priced its IPO at $11 a share. You're the analyst asked whether your firm should recommend it.

It's late 2009. Greece's newly elected government just revealed the country's actual budget deficit is far larger than previously reported — roughly double earlier official figures. You manage a macro fund holding Greek government bonds, previously considered about as safe as any other Eurozone sovereign debt.

It's late 1999. You have $10,000 to invest and are choosing between two very different companies: Microsoft, the most valuable company in the world and a dominant, wildly profitable software monopoly — and Amazon, an online retailer growing revenue explosively while losing more money every year it operates.

It's Monday, September 15, 2008. Lehman Brothers has just filed the largest bankruptcy in U.S. history. You manage a diversified fund with meaningful exposure to financial-sector stocks and short-term credit markets. Your phone hasn't stopped ringing since 6 a.m.

It's mid-January 2021. You're an individual retail trader who's been following GameStop discussion on Reddit's r/wallstreetbets for weeks. The stock has climbed from around $20 to $40 as the community organizes around an unusual fact: more than 100% of GameStop's available shares have been sold short.