The first worry is about direct competition for things that are in more or less fixed supply: geopolitical supremacy, the world's oil and raw materials, the status and perks that come with being the issuer of a trusted international currency.

ECONOMIST: A game of catch-up

Though the Petersiks in the past have made revenue through paid writing jobs and private design consulting, the majority of their income now comes from advertising on the site - either through automatically generated Google ads, or through direct site sponsors, which often include design and home supply companies such as the Tile Shop.

BBC: One couple's mission to find a better work/life balance