ETFs — the Instrument

What an ETF is

A fund trading like a stock that holds a basket (index, sector, commodity, strategy). One purchase = instant diversification across the basket. Key mechanics: expense ratio (annual fee, e.g., 0.03% for core index ETFs vs 1%+ for active funds — fees compound against you exactly like returns compound for you), tracking difference (how closely it follows its index), and liquidity (spread + volume).

Index funds — the base case

Broad-market index ETFs capture the market's return at near-zero cost with no manager risk. Bogle's arithmetic: after fees, MOST active funds underperform their index over 15+ years (SPIVA data confirms it every year) — so the index IS the default rational holding, and any active choice (single stocks, sectors, factors) must be justified AGAINST that baseline, not just against zero.

The ETF zoo — reader beware

Beyond core index funds: sector ETFs (concentrated bets), leveraged ETFs (daily-reset compounding — decay makes them day-trading tools, NOT holds), inverse ETFs (short bets, same decay), thematic ETFs (narrative baskets, often launched near theme peaks). The wrapper is neutral; the CONTENT needs the same analysis as any position — plus the fee and the tracking error.

Sources

• The Little Book of Common Sense InvestingJohn Bogle
• Exchange-Traded Funds (ETF)Investopedia