I wrote last week about trends that can’t continue and noted that I would be looking at more of them through December. First, though, it makes sense to consider exactly what it is that makes a trend unsustainable.

Why can’t something go on forever?

As the industry that led us to disaster in 2008, housing has had a long road back. You can make a good argument that, until the housing market returns to normal, the economy hasn’t really recovered. While not a defining indicator, a healthy housing market is a necessary condition for recovery.

I last looked at housing in June, so it’s time for an update. The news is actually quite good, despite some of the headlines recently. 

I have two reasons for writing a post on gratitude today: The first is that I have much to be grateful for (I plan to write a longer post about this next week as we approach Thanksgiving), and the second is that I have been in meetings all day and am too short on time to finish the housing market post I had planned. You’ll get that tomorrow.

“If something can’t go on forever, it will stop.” — Herb Stein

When you think about it, we really do live in an age of miracles. Less than 24 hours ago, I was in London, but I slept in my own bed last night and am back at work in Boston today. While in Europe, I kept in touch with my family via video-call and simply pulled out my credit card to pay for things. It was all astonishingly seamless.

For the past two days, I’ve been in London at a J.P. Morgan European investment summit, and a fascinating time it has been.

As investors, it's not so much the things we don't know that we need to be mindful of, but the things we don’t even know we don’t know. For Americans, how things really are in the rest of the world can easily fall into that category, so it’s been interesting to get some international perspective over the last couple of days.

Here are three of my key takeaways.

The big news today is that, after two consecutive quarters of declining growth, Japan has fallen into recession. The Japanese economy was down 1.6 percent in the third quarter, following a 7.3-percent decline the previous quarter.

Along with being aware of external problems, investors need to acknowledge one of the pending headwinds for the U.S. stock market: the potential for corporate profit margins to decline.

Today, I want to summarize a great analysis by Baijnath Ramraika and Prashant Trivedi, which suggests that margins can’t continue to climb.

One problem I have with satellite radio is that it makes me confront my own mortality every day. Let me explain. When a song comes on, I think, Oh, I remember that; it must have come out about five years ago. But when I look at the screen, the song is invariably from the 1990s or (in particularly bad cases) from the 1980s. Perhaps I’m not as young as I feel.

That said, a bit of perspective—which is a kinder word for age—is beneficial in the economics and investing game.

I’m currently reading Thinking, Fast and Slow by Daniel Kahneman—a great book on how we make decisions, and how we can learn to make better ones. Its assertions are shocking, and even insulting, but they’re all the more useful for it. (Look for a full review here soon.)

One of Kahneman’s points is how bad we are at remembering what we thought at a given time—and how we tend, in retrospect, to think we were much more prescient than we actually were.

I mentioned yesterday that employment numbers are much stronger than most people are giving them credit for. The one exception is wage growth, which, as a statistic, has some weaknesses.

Today, I want to talk about those weaknesses and look at some numbers that paint a rosier picture.