In this episode of The 100-Year Thinkers, Robert Hagstrom explains why modern portfolio theory pulled investors away from business analysis and toward portfolio math. In this episode, Hagstrom, Matt Zeigler and Bogumil Baranowski discuss Markowitz, beta, efficient markets, Warren Buffett, Charlie Munger, business-driven investing, owner earnings, benchmarks, and why thinking like a business owner changes how investors understand risk.
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Topics covered:
Why Hagstrom thinks modern portfolio theory changed investing’s objective
The difference between volatility, variance and real investment risk
How Benjamin Graham and John Burr Williams framed risk around intrinsic value
Why beta became the dominant shorthand for risk
How the 1973-74 bear market helped institutionalize modern portfolio theory
Why Berkshire preserved the business owner’s lens
The “cathedral and casino” distinction between owning businesses and trading stocks
Owner earnings, return on invested capital and cost of capital
Why business owners often make better long-term equity investors
Look-through earnings and building a “mini Berkshire”
The difference between making money and beating a benchmark
How benchmarks can distort investor behavior
Why knowing yourself and your clients matters in portfolio construction
Timestamps:
00:00 Robert Hagstrom on why risk is not volatility
00:40 Business-driven investing vs portfolio math
02:42 How modern portfolio theory defined risk as variance
06:38 Graham’s margin of safety vs Markowitz’s definition of risk
09:44 Sharpe, beta and simplifying portfolio risk
12:51 Why the 1973-74 bear market helped MPT take over
16:20 Why MPT became institutionalized without proving it could beat the market
18:53 Buffett, Keynes and concentrated investors violating MPT
22:53 Stocks as businesses and Buffett’s cathedral vs casino
30:01 Business analysis, owner earnings and return above cost of capital
36:41 Look-through earnings and running a mini Berkshire
41:34 Making money vs outperforming a benchmark
47:30 Why Berkshire’s public and private businesses shaped Buffett
50:05 How investors can start applying the Buffett way
54:05 Bogumil on how investing theory becomes accepted truth
58:09 Why direct ownership creates responsibility and conviction
01:00:15 Investor know thyself and the limits of outsourcing caring
01:03:35 Finding the right clients for a business-owner investing approach