Rebalancing asks an investor to sell some of what's working and buy more of what isn't. That's exactly why it's universally recommended and almost never actually done.
Rebalancing means periodically restoring a portfolio to the proportions its owner originally set. Over time, the holdings that do well grow into a bigger share of the total, and the ones that lag shrink. Left alone, a portfolio drifts away from its intended shape, and that drift isn't neutral - it moves steadily toward whatever has recently risen, meaning the investor ends up most heavily exposed to whatever has already run the furthest, without ever deciding that's what they wanted.
The mechanics fit in one sentence. An investor sets a target set of proportions, checks periodically whether the real proportions have drifted materially away from them, and if so trims what's grown and adds to what's lagged to restore the balance. This can run on a calendar, at fixed intervals, or on a threshold, whenever a holding drifts past some defined band. Either works fine, and the choice between them matters far less than actually following through and doing it.
Following through is the whole difficulty, because rebalancing runs against every instinct. It asks an investor to cut back on whatever's been rewarding them and add to whatever's been disappointing them - the exact opposite of what feels natural. The winning holding feels like the one to keep. The struggling one feels like the one to dump. Rebalancing insists on the reverse, and offers no guarantee whatsoever that the reversal will be vindicated.
The justification isn't that the lagging holding will necessarily bounce back, and any pitch for rebalancing that implies otherwise is overselling it. The justification is that the portfolio's proportions were set for reasons, and those reasons haven't changed just because prices moved. If an investor decided a given allocation was the right level of exposure, letting that exposure balloon through price appreciation means holding a level of exposure they never actually chose. Rebalancing isn't a bet on reversion. It's maintenance of a decision already made.
This framing clarifies what rebalancing does and doesn't accomplish. It doesn't reliably boost returns - the evidence there is murkier than its advocates sometimes admit. During a stretch when one holding climbs for years running, an investor who rebalanced away from it will have earned less than one who didn't, and no theory changes that arithmetic. What rebalancing reliably does is control risk, keeping a portfolio from becoming, through sheer inaction, far more concentrated and exposed than its owner ever meant it to be.
That unintended concentration is worth sitting with, because it's how a lot of investors discover they weren't diversified after all. A holding that's performed exceptionally well for several years can grow into a share of the portfolio its owner never would have chosen on purpose, and they may not notice until it falls. That's when they discover their portfolio's fate is tied to a single position - not because they decided it should be, but because they never decided anything at all. Not deciding is itself a decision, and it's one of the pricier ones.
Rebalancing is also one of the few disciplines genuinely indifferent to style. A value investor, a growth investor, an index investor, a core-satellite investor - they all face the same drift and benefit from the same fix. The specific target proportions differ wildly; the need to maintain them doesn't. That universality is unusual, and it suggests rebalancing sits in a different category from the styles it serves. It's not an approach to investing. It's the upkeep every approach requires.
There are costs worth weighing honestly rather than brushing aside. Rebalancing generates transactions, transactions generate fees and, depending on circumstances, tax bills, and rebalancing too often can eat up more in costs than it saves in risk control. That argues for restraint rather than abandonment: rebalancing on a sensible schedule, or once drift has become material rather than trivial, captures most of the benefit at a fraction of the cost.
There's a useful way to make the discomfort more bearable: recognize what rebalancing actually is, mechanically. It isn't a judgment call about which holding looks attractive now and which doesn't - an investor who treats it that way has smuggled forecasting back into a process built to avoid it. It's simply restoring a decision already made. The investor isn't predicting the lagging holding will recover; they're noticing that their intended exposure has drifted and correcting it. Seen this way, rebalancing requires no view about the future at all, which is exactly what makes it doable. An investor who could only rebalance when they felt confident about the lagging holding would rarely rebalance, since confidence is precisely what a lagging holding fails to inspire. Strip out the need for confidence, and the discipline can actually survive contact with reality.
At VESTFY™, rebalancing is presented as the clearest example available of a discipline that's trivial to understand and genuinely hard to perform. An investor who can bring themselves to trim what's working and add to what isn't has shown something valuable about their ability to follow a plan when following it feels wrong - and that ability is what every style ultimately rests on.