What happens when all eggs share one basket?
Before the cure, the disease — told through the most instructive corporate collapse in modern memory.
The Enron lesson
In 2001, Enron — a celebrated US energy giant, repeatedly crowned an innovation leader — collapsed into bankruptcy within months as massive accounting fraud surfaced. The stock, above $90 at its peak, went to effectively zero.
The catastrophe inside the catastrophe: thousands of Enron employees held their retirement savings heavily in Enron stock. When the company died, they lost their jobs AND their savings in the same stroke — income and wealth, one basket, one match. Many were diligent savers who did everything "right" except one thing: concentration.
Why concentration is a different KIND of risk
Unit 3 taught that a single company can go to zero permanently while broad baskets historically recover. Concentration means exposing your entire outcome to the zero-capable animal. And the risk hides behind precisely the things that feel like knowledge: employees "knew" Enron (familiarity), it had risen for years (recent history as proof — a Course 3 bias in the wild), everyone around them agreed (one dinner table, one opinion). Confidence concentrates portfolios; arithmetic diversifies them.
The recovery math makes concentration unforgivable at the extreme: a diversified basket's −30% crash needs +43% to heal — historically achievable; a single position's −100% needs infinity. Some losses close; that one doesn't.
The quiet everyday versions
Full Enron is rare; mild Enron is everywhere — savings in your employer's shares, portfolio all in one hot sector, everything in one country's market (home bias — even the macro course's geography lesson applies). Same structure, softer dose.
In the data
The mild version is measurable. A fund's profile breaks its money down by sector, by asset class and by region; here is the S&P 500 fund, SPY:
Technology read 40.1% on 28 September 2026 — five hundred names whose largest single neighbourhood is two fifths of the basket. The last two rows answer the other two concentration questions raised above, asset class and geography: over 99% in US stocks, over 99% in North America.
Try it now
- Name the double loss Enron employees suffered and why holding YOUR employer's stock repeats the structure.
- Measure the mild version in the safest thing you own, with SPY's eleven sectors in the table above. Find the largest, then add the smallest ones up one at a time until their total passes it. On 28 September 2026 it took nine of the other ten sectors to outweigh Technology alone — in a fund whose entire selling point is that it holds five hundred companies. Count it again on the table as it stands today.
- Then check the other two axes, the last two rows of the table: over 99% in US stocks, and the same again by region. Diversified across companies, concentrated in one asset class and one country: three questions, and the fund only answers the first.
- Spot the mild version in your own savings: all of it in one booming sector — which Course 3 bias makes that feel safe?
- One sentence: why is −100% mathematically different in kind, not just degree?