The index is at a record. My phone is ringing anyway.

The call comes on a Tuesday, a few days after whatever that week's bad story is. The client is sixty-eight, retired, and has done nothing wrong. He has read three articles, one of which contradicted the other two, and he wants to know whether we should be doing something. Nine times out of ten, we already did it in April, on a quiet morning, when nobody was asking.

The concentration is the part that deserves attention. The ten largest companies in the S&P 500 are close to forty per cent of the index, up from roughly a fifth in 1995. Their share of earnings has risen too, so this is not pure speculation: the biggest companies are genuinely more profitable than the average company was thirty years ago. But the index has become a narrower bet than the one most people believe they own.

Two things drive it. Market-cap weighting means every dollar into an index fund buys more of whatever is already largest, and passive funds now hold more American equity than active ones. And the largest companies have the margins to keep buying back stock, which lifts earnings per share without any additional growth. Neither mechanism is a scandal. Both concentrate risk quietly, without a single decision by the person holding the fund.

The arithmetic is simple and worth doing. If ten companies are forty per cent of a portfolio and they fall thirty per cent while everything else stands still, the fund is down twelve per cent. That is not a crash. It is an ordinary bad year for a handful of businesses, arriving in a portfolio the client was told was diversified.

What matters is not the headline but the horizon. Money needed in the next three years should not be in equities at all, whatever the index is doing. Money needed in twenty should not be moved because of a Tuesday. Most of the damage done to family portfolios over the last thirty years was not done by markets. It was done by selling in March 2009 and buying back the following June.

So we do four things, none of them clever. We hold three to five years of spending in Treasury bills and short bonds. We keep a meaningful slice outside the largest ten: equal-weight, international, smaller companies. We rebalance on thresholds rather than dates, and take the tax loss when it is available. And we decline to add to the position that is already forty per cent of the index.

On the call, we ask three questions. Has anything in your life changed? Has the plan changed? Is anything actually broken? If the answers are no, the correct action is no action, and saying so is the job. The portfolio does not read the news. The man holding it does.