In the stock market, behaviouralist commentators warn of the dangers of “anchoring” – being so influenced by where prices have been recently it obscures objective assessment of valuation and future prospects.

One wonders whether this has been at work in the oil industry too. In recent years the oil price has stayed fairly consistently within a broad range of between $80 and $120. So much so that a consensus formed that this is the "right" price. Hence the scale of the shock - entirely unpredicted by all those earnest economists and forecasters - when Saudi Arabia initiated a price war last year.