Selling in a fall is the most expensive thing investors do

Everything here earned its place by changing an outcome. Nothing about selling during a downturn is included to round the number up.

The behaviour gap is measurable

Studies comparing fund returns with the returns actually earned by investors in those funds consistently find a gap. The cause is timing: money arrives after good periods and leaves after bad ones. That gap is a self-inflicted cost and is often larger than the fees people worry about.

The direction of that finding is well supported and the measured size is contested, since it moves considerably with the method used and some estimates are inflated by how flows into newly launched funds are treated.

A fall is not a loss until you sell

A decline in price is a change in valuation; the loss becomes permanent only when the holding is sold. Selling also creates a second decision — when to return — which is harder and usually made late. Investors who sold in major downturns frequently missed the sharpest recovery days, which cluster near the bottom.

That missed-best-days illustration is weaker as an argument than it looks, because the worst days cluster in the same weeks; the defensible version is that neither is predictable and being absent removes the recovery you were waiting for.

Falls are a normal feature

Substantial declines occur regularly across market history and are the reason equities have delivered a premium. Expecting them and planning for them is different from predicting them. An allocation that cannot survive an ordinary decline is misallocated rather than unlucky.

For most people, not everyone is in a position to hold through one, and where the money is genuinely needed soon or the income behind it has stopped, selling can be the correct decision rather than a failure of nerve.

Write the plan while calm

A one-page statement of what you hold, why, and what you will do in a fall is the most effective defence available. The commitment matters because judgement degrades precisely when it is needed.

On an ordinary week, reading your own reasoning during a decline is more persuasive than reading anyone else's. A written waiting period, in which nothing is sold for a set number of days after the decision is made, costs nothing and removes most of the trades that would otherwise happen inside a single afternoon.

Reduce the exposure to noise

Checking balances frequently increases the chance of seeing a decline and acting on it. Financial news is produced continuously and is optimised for attention rather than for long-horizon decisions. Quarterly or annual review is sufficient for a portfolio designed for decades.

Portfolio apps are built to be opened often, and switching off the price alerts is a more reliable intervention than resolving to look less.

Adjust the size of it until it is something you would actually do tired.

The middle options nobody offers you

Between holding everything and selling everything sit pausing new contributions, selling a defined portion, or moving one holding, and any of them does less damage than the all-or-nothing choice panic presents. If the urge to act is really about the allocation being too risky for you, the honest fix is a permanently smaller equity share rather than a temporary exit with no defined return date.

Where it helps most, making that change during a fall does lock in part of the decline, which is a genuine cost and still preferable to a full exit followed by several years in cash. Where the pressure to sell comes from needing the money rather than from fear, the useful conversation is about income, debts and timing, and a portfolio decision will not answer it.

Everything above, in order of what to do first

1. The behaviour gap is measurable. Studies comparing fund returns with the returns actually earned by investors in those funds consistently find a gap.
2. A fall is not a loss until you sell. A decline in price is a change in valuation; the loss becomes permanent only when the holding is sold.
3. Falls are a normal feature. Substantial declines occur regularly across market history and are the reason equities have delivered a premium.
4. Write the plan while calm. A one-page statement of what you hold, why, and what you will do in a fall is the most effective defence available.
5. Reduce the exposure to noise. Checking balances frequently increases the chance of seeing a decline and acting on it.
6. The middle options nobody offers you. Between holding everything and selling everything sit pausing new contributions, selling a defined portion, or moving one holding, and any of them does less damage than the all-or-nothing choice panic presents.

The takeaway

Write down now what you will do in a thirty per cent fall. You will not think clearly then.

Small and repeatable beats ambitious and abandoned, almost every time.