“Buy what you know.”

It’s one of the adages of investing, and it has plenty of intuitive appeal. After all, the familiar seems inherently less risky. It’s no wonder that many investors heavily tilt their portfolios toward the stocks and bonds of their home country. This is known as “home bias.”

U.S. investors sometimes think they can get all the global diversification they need by owning shares of U.S.-based multinational companies. And that may seem like the best of both worlds: international diversification without ever leaving the friendly confines of home.

The potential pitfall is that, as Vanguard research has suggested, the performance of a company’s shares tends to be highly correlated to its domestic market, regardless of where that company conducts most of its business.

Americans aren’t alone in being portfolio homebodies. Vanguard found that in a range of developed countries—Australia, Canada, Japan, and the United Kingdom, as well as the United States—investors held more in domestic stocks than they would if they tracked a globally diversified, market-weighted benchmark.

Why home bias exists

Vanguard’s Investment Strategy Group identified a range of reasons why investors might not embrace global diversification, including concerns about currency risk and an expectation that their home country will deliver outsized returns.

One factor we identified—preference for the familiar—seems particularly relevant. With so much global uncertainty about geopolitics, monetary policy, and the economic outlook, it’s understandable why investors may not want to stray too far from home.

But in their aversion to the unknown, investors can end up increasing, rather than lessening, their risks. That’s because they’re sacrificing broad global diversification—one of the best ways I know of to help control risk.

In many cases, individual country markets are much less diversified than the global market in total. Global investing, then, can be an answer for investors who want to reduce concentration risk. That can include overconcentration in a particular country, region, or industry.

And the good news is that global investing is easier than ever, thanks to the wide availability of low-cost, internationally diversified stock and bond funds. It’s possible, in a sense, to own the whole world with just a couple of funds.

Expanding our opportunities

A key to overcoming home bias is reframing the way we look at investing outside our home countries. Take, for example, automakers or pharmaceutical companies. There are well-regarded firms in both industries located throughout the world. Over the next five years, nobody can know for sure whether a Japanese or U.S. or European company will produce a popular new sedan that outsells the competition or come up with new treatments to combat illness. So why not own them all? And that includes their bonds along with their stocks.

Full global diversification also allows you to capitalize on opportunities in both developed and emerging economies. Betting on which individual country­—let alone company—will be the next market darling can be a fool’s errand.

A better choice can be to harness the potential of all markets. In my personal investment account, I have an emerging markets position that complements my developed-market holdings. Global diversification can help control risk, and it can also expand our set of opportunities among stocks and bonds.

Ultimately, I believe we have the best chance for investment success by giving ourselves more opportunities, not fewer. Own the whole haystack and you never have to worry about finding the needle.

Notes:

All investing is subject to risk, including the possible loss of the money you invest. Diversification does not ensure a profit or protect against a loss.

Investments in bonds are subject to interest rate, credit, and inflation risk.

Investments in stocks or bonds issued by non-U.S. companies are subject to risks including country/regional risk and currency risk. These risks are especially high in emerging markets.