December is often the time of retrospection and yearly wrap-ups, with stories recapping events of the last year and looking forward to new opportunities. In the finance space, you’ll find endless collections of the top performers of the year and forecasts for the one to come. While that’s all interesting and comforting in its own ritualistic way, this holiday season I decided to revisit a bold question that’s much bigger than short-term market news cycles:

What do the most efficient portfolios in history have in common?

Truly understand that answer, and much of the market noise that worries you from day-to-day and year-to-year loses its power over not only your emotions but also your account balances. So if you’ve ever wanted to think beyond your investing assumptions and explore the data for proven ways to approach timeless portfolio problems, grab a cup of coffee and pull up a chair. This article is for you.

Buried in an otherwise mind-numbingly boring regulatory filing released recently was a seemingly innocuous line item that most people would not give a second thought. Sometime in the second quarter, Berkshire Hathaway invested a comparatively tiny 0.3% of their total portfolio into just a single new company. No big deal, right?

But it wasn’t just any company. After spending decades as perhaps the most respected and widely-cited critic of gold as an investment, Warren Buffett bought 21 million shares of Barrick Gold — one of the largest gold mining companies in the world. It was so out of character that the financial world immediately did a huge double-take. The headline from Bloomberg pretty much speaks for itself:

Berkshire Makes a Bet on Gold Market That Buffett Once Mocked

As one might expect, investors on both extremes of the gold-appreciating spectrum are furiously debating what this all means. Buffett’s closest gold-averse followers are circling the wagons and dealing with a lot of cognitive dissonance, while gold bugs are enjoying dishing out some playful jabs after years of being on the receiving end. Lost in the middle is a vast sea of normal investors watching the news and searching for actionable information.

This article is for that last group just wanting to know the truth about gold and what it can (and can’t) do for their own portfolios.

In the world of investing, it seems most people’s energy is focused squarely on stocks. Massive amounts of research goes into stock investing every day and even casual investors have an incredible amount of information at their fingertips. Combine that wealth of data with a long term growth pattern in the stock market since 2009 that means anyone who has been in the market less than ten years has no recollection of a single meaningful bear market, and stocks are so ingrained on our collective investing consciousness that many people don’t give other assets a second thought.

As a result, while bonds were once staples of any self-respecting asset allocation lots of investors just aren’t into them like they used to be. Some of it is definitely recency bias, and I think another factor is that many people don’t truly understand how bonds work. But I’ll concede that the bond market is also different than it was more than a decade ago, and I can understand why people might think twice about relying too much on historical data. After all, bonds sound like awesome choices when they paid 10% interest, but consistent declining rates over time surely boosted any backtested numbers while depressing yields today to something a lot less desirable. So it’s no surprise that I see questions along this line all the time:

With record low interest rates today that are even negative in some situations, what’s the point of having bonds in a portfolio at all?

That’s a very good question. And the full answer is kinda complicated and includes some advanced finance mechanics that fly under the radar even for very experienced investors. But explaining complicated concepts is kinda my thing, so let’s talk about a little thing called bond convexity.