One of the themes in the book and the blog has been that by choosing what we eat we can lessen our impact on Earth. I'd previously suggested that eating fishes like sardines could be a sustainable food choice. But the rapid crash of US West Coast sardine fisheries took me a bit by surprise. Read more about this and its consequences at this Pew briefing.
The take-home message: constantly reevaluate your assumptions and modify behavior based on new data.