A portfolio's day-to-day behavior comes less from which securities it holds than from the proportions held in each broad asset class.
Asset classes move for different reasons
Stocks represent ownership and their prices respond to expectations about earnings and growth, while bonds represent lending and respond primarily to interest rates and credit conditions.
Because the drivers differ, the two classes frequently move in different directions or by different magnitudes in the same conditions.
Cash and short-term instruments respond mainly to short-term rates, which makes them the most stable in price and the most exposed to inflation.
Correlation is what allocation exploits
Combining assets that do not move identically produces a portfolio whose swings are smaller than the weighted average of its parts.
That reduction in variability comes from the imperfect relationship between the holdings rather than from any of them being individually safer.
Correlations are not fixed, and they tend to rise during periods of severe market stress, which limits how much protection the effect provides exactly when it is most wanted.
That instability is why allocation is described in terms of long stretches rather than single episodes. The relationships hold on average across years while breaking down in particular weeks.
Individual selection matters less than proportions
Two portfolios holding different large-company stocks will behave similarly if their overall stock exposure is similar, because the class-level movement dominates.
Changing the stock and bond split, by contrast, changes the portfolio's behavior substantially without touching a single security choice.
That relationship is why allocation is decided first and holdings are chosen afterward to implement it.
Drift changes the allocation without a decision
Because asset classes grow at different rates, the proportions move away from their targets over time on their own.
A portfolio left alone through a strong equity period ends up holding more stock than intended, and carrying more variability than the plan called for.
Rebalancing restores the intended proportions, which mechanically means selling what has grown and buying what has not.
How often that is done is itself a choice, since frequent rebalancing tracks the target closely while incurring more transactions, and infrequent rebalancing allows larger drift between checks.
The right allocation is a personal input
The appropriate mix depends on the time until the money is needed, the household's capacity to absorb a decline and its tolerance for seeing one.
Those are individual circumstances rather than market questions, which is why no allocation is correct in general.
Nothing here is a recommendation for any particular mix, and the decision is one a qualified advisor is positioned to address for a specific situation.