What Is Diversification? Why You Should Not Put All Your Eggs in One Basket

What you will learn in this lesson

An old proverb says, "Do not put all your eggs in one basket." That sentence sums up one of the most important ideas in investing: diversification. In this lesson you will learn exactly what diversification means, why it works, what the key concept of "correlation" is, and how to build a genuinely diversified basket in Iran's market. No prior knowledge is needed; every term is defined right here.

Definitions

Portfolio (basket of assets): the whole collection of assets a person holds, for example some money in a bank deposit, a few gold coins, some shares on the stock exchange, and a house. Taken together, we call all of these the "basket."

Diversification: spreading money across several different assets instead of putting it all into one. The goal is to reduce the danger of loss, not necessarily to increase returns.

Risk: the chance that the actual return differs from what you expected, especially in the direction of loss. If you are new to this idea, first read the previous lesson, Risk and Return.

Correlation: a measure of how far two assets move "together," up and down. Its value ranges from minus one to plus one:

• Positive correlation (near +1): the two assets usually rise together and fall together.
• Negative correlation (near -1): when one rises, the other usually falls.
• Correlation near zero: the behaviour of the two assets has little to do with each other.

Correlation is the heart of diversification: diversification truly works only when the assets in the basket do not move together.

The mechanism: why diversification lowers risk

Every asset has its own good and bad days and years. If all your money is in one asset, your fate is tied entirely to that single holding; one piece of bad news shakes your whole capital. But if you spread the money across several assets that do not turn bad at the same time, the loss of one is offset by the gain of another, and the swings of the whole basket become gentler.

Here is the subtle point: simply owning "several" assets is not enough. If all five assets in the basket collapse together in one shock, you effectively hold one asset. The benefit of diversification comes from low correlation, not from the number of holdings.

Diversification reduces one kind of risk and not another:

• Specific risk (unsystematic risk): a danger that threatens only one company or asset, such as the bankruptcy of a particular company. This risk can be largely neutralised through diversification.
• Market risk (systematic risk): a danger that hits the whole market at once, such as heavy inflation, war, or a sudden jump in interest rates. Diversification does not remove this risk, because it affects almost everything simultaneously.

A numerical example (hypothetical)

The figures below are entirely hypothetical and for teaching only. Suppose you have 100 million tomans and two assets in front of you:

• Asset A, stocks: returns +50% in a boom year and -30% in a crisis year.
• Asset B, gold: returns +10% in a boom year and, because it is a safe haven, +40% in a crisis year.

Case one, everything in stocks: in a boom year your capital becomes 150 million and in a crisis year 70 million; that is a very large swing, from +50% to -30%.

Case two, half stocks and half gold: in a boom year the return is the average of 50 and 10, that is +30%; and in a crisis year the average of -30 and +40, that is +5%. Even in the bad year the diversified basket earned a small gain and never fell into loss.

Compare them: the single-asset basket ranged between +50% and -30%, while the diversified basket stayed between +30% and +5%. The range of the swing shrank sharply. That is what diversification gives you: a calmer ride, not necessarily the highest possible return. Note that this pleasant result comes from the negative correlation between gold and stocks in this example; had both collapsed together, diversification would not have helped.

In Iran's market

An Iranian household usually chooses among these assets: bank deposits, gold and coins, the dollar and other currencies, shares on the stock exchange, housing, and sometimes cars. To build a truly diversified basket, you must watch how these correlate:

• The dollar, gold, and coins have high long-run correlation, because all three are shelters against the falling value of the toman. Buying all three at once is more like one big bet on "a weaker toman" than genuine diversification.
• The stock market behaves in a more complex way: part of it rises with inflation and the dollar, but company profits, policy, and market sentiment also matter, so its correlation with gold is not constant.
• A bank deposit has a fixed nominal return and stays calm against market swings, but in high inflation its real value erodes.
• Housing moves slowly and trades rarely; its day-to-day correlation with other markets is low, but it is slow to turn into cash.

A simple route to diversification for someone without the time or knowledge is investment funds, which spread the money across dozens of assets on your behalf. For the professional framework of arranging and rebalancing this basket, see the Asset Allocation lesson.

Common mistakes

• "Diversification means buying several things." No; if those several things are highly correlated (like the dollar, gold, and coins), you effectively hold one asset. What matters is different behaviour, not the count.
• Over-diversification. Spreading money across dozens of shares and assets makes the basket unmanageable and costly, and adds no extra return. Beyond a certain point, more diversification brings little benefit.
• "Diversification prevents every loss." No; diversification reduces specific risk, but against systematic risk (broad inflation, war, a whole-market crisis) that drags everything down together, it is not a complete shield.
• "Diversification increases returns." The main goal of diversification is to smooth the swings and reduce risk, not to guarantee a higher return. Sometimes diversifying means giving up the highest possible gain in order to stay away from the worst possible loss.

Summary

Diversification means spreading money across assets that do not rise and fall together, so that the loss of one is offset by another and the swings of the whole basket calm down. The key is low correlation, not merely a large number of assets; and remember that diversification tames specific risk but not whole-market risk. In Iran's market, be careful that buying the dollar, gold, and coins at the same time is not real diversification. In the previous lesson we covered Risk and Return; the next lesson takes diversification to the level of arranging the basket and making practical decisions. The full set of lessons is available in the Sahmino Academy.