If Buffett says put all your eggs in one basket and watch it, why does portfolio theory spread them, and what does a mean-variance investor want?
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One basket versus a systematic portfolio
Record Buffett's put-all-your-eggs-in-one-basket advice and the counterpoint for an investor who cannot pick the right basket, stating the goal as responsible systematic investing rather than beating the market.
Three uses of portfolios
List diversification, focused sector bets without single-firm risk, and a tailored risk-reward trade-off, using the information-technology sector portfolio as the worked example of a focused bet.
Reward as expected return, risk as standard deviation
State both measures as assumptions, list the alternatives (upper quartile, 5th-percentile loss), and record the upside-risk objection together with the symmetric-distribution case where it makes no difference.
The mean-variance investor
Write the assumption that investors like higher expected return, dislike higher variance and judge only the overall portfolio, and frame each added stock by its contribution to portfolio return and risk.