The impact of a change at the top should not be overstated. A new face leading a vast organisation has about the same short-term effect as repainting the headquarters a different shade of beige. This is particularly the case for big, defensive retailers. Without the swings of the business cycle to move things along, genuine shifts in profitability or market share unfold over the course of many years.

Wal-Mart is a case in point. The world’s largest retailer made the surprise announcement on Friday that chief executive Lee Scott would stand down in February after eight years at the top and three decades with the company. Mike Duke, head of international operations, will become only the fourth Wal-Mart CEO in the group’s history.