Rebalancing rules are easy to state: sell what’s run up, buy what’s lagged, return to target weights. They’re much harder to actually follow after a quarter where “what’s lagged” is down 20% and every instinct says wait for a recovery before adding more.
That instinct is precisely what rebalancing is designed to override. The discipline isn’t a market call — it’s an admission that nobody, including the person doing the rebalancing, reliably knows which asset recovers first. A fixed schedule (quarterly, or a band-trigger around target weights) removes the decision from a moment when judgment is least trustworthy.
The mechanical version isn’t exciting to write about, which is probably why it works.