This is a simplification in order to make the high-level point. It’s likely that blockchain-based services like the one I am describing will use a mixture of on-chain and off-chain computing. More demanding computing tasks — even things like matching participants in a market — are probably too demanding to be run on the blockchain. However, even computing off the chain can be made trustworthy by reference to the blockchain — e.g. A scheme where the off-chain process must offer a cryptographic proof to the blockchain that it was performed correctly. I use the phrase “set in place & guaranteed” for this reason.