Rebalancing DisciplineCopy Anchor Link

Rebalancing DisciplineCopy Anchor Link

Rebalancing is the rule-bound restoration of a portfolio's drifted weights back to policy, and it is the mechanism that keeps an asset allocation alive against the market's tendency to concentrate winners. The corpus offers both the textbook definition and a sharp practitioner's dissent over when the rule should bind.

The CFA curriculum defines the problem precisely. As a portfolio is constructed and its value changes, the weights of the asset classes gradually deviate from the policy weights in the strategic asset allocation — a process referred to as drift. The remedy is a policy: "Periodically, or when a certain threshold deviation from the policy weight (the bandwidth) has been breached, the portfolio should be rebalanced back to the policy weights. The set of rules that guide the process of restoring the portfolio's original exposures to systematic risk factors is known as the rebalancing policy." Its importance is stated as a floor, not a ceiling: "Even absent a formal risk budget, formulating a rebalancing policy is an important element of risk management." In the portfolio-management process it lives in the feedback step, alongside monitoring and performance review.

The behavioral rationale for having a rule is Dalio's. Across every decade there were years that ran opposite to the decade's character, and to survive them one had to time the ins and outs, or "faded the moves (i.e., bought more when prices fell and sold more when prices rose), or had a balanced portfolio that would have held relatively steady through the moves. The worst thing would have been to go with the moves (sell after price declines and buy after price increases)." Rebalancing is "fading the moves" mechanized: it forces the sale of what has risen and the purchase of what has fallen, inverting the natural impulse to chase.

The dissent is that a mechanical rule can destroy the very thing value investing compounds. Buffett's 1988 letter: "when we own portions of outstanding businesses with outstanding managements, our favorite holding period is forever. We are just the opposite of those who hurry to sell and book profits when companies perform well but who tenaciously hang on to businesses that disappoint." Howard Marks (January 2022) presses the same point against trimming a winner on price alone: "Great compounders are extremely hard to find, so it's usually a mistake to let them go", and selling decisions "should be based on the outlook for the investment – not the psyche of the investor."

The reconciliation is that the two disciplines govern different objects. Rebalancing is a rule over asset classes, where drift is a risk problem — the portfolio silently becomes more exposed to whichever class has run. The value investors' refusal to trim is a rule over individual holdings, where the question is relative merit, or what Marks calls "the discipline of relative selection": most portfolio decisions are comparative, and a position is sold not because it rose but because it now ranks below an alternative.

Both, in their own domain, are defenses against permanent-loss-of-capital — the former against the loss that comes from unwitting concentration, the latter against the loss that comes from selling the few assets that carry the portfolio. The failure mode is symmetric: mechanical rebalancing into a falling cycle bottom, and never-rebalancing concentration at a top.

SourcesCopy Anchor Link

• textbooks/markdown/investment-textbooks-pdfs__CFA LV1 2025 - Volume 09 - Portfolio Management.md
• investor-letters/DalioBridgewater/Letters-Markdown/Paradigm Shifts (2020).md
• berkshire-hathaway/Letters-Markdown/1988 - Letter to Shareholders.md
• howard-marks/Memos-Markdown/Selling Out.md