They have seen the turmoil at Tesco following the exit of Sir Terry Leahy.
And Sainsbury's is losing the man who has overseen a turnaround of the business since joining from Marks & Spencer a decade ago.
In 2004 customers were deserting the chain in droves unhappy with limited product availability and poor quality.
By early 2014 it was the only big grocer in growth having expanded sales for 36 quarters and was battling Asda for the market number two spot.
Sainsbury's matched market leader Tesco's forays into the lucrative new areas of convenience stores and online retailing but avoided its often expensive forays overseas.
Taking into account dividends, Sainsbury's shares have returned around 100% in the last decade, well ahead of its rivals.
Mr King managed to combine commerce and ethics, leading the way in stocking fair trade goods and dodging the horse meat scandal. He showed an ability to anticipate popular attitudes with sponsorship of the Paralympic Games last summer.
His decision to forgo a pay-off (while retaining lucrative share awards) shows a sensitivity towards the public mood. He has also been vocal about the pressures on household incomes.
Mr King has been linked with Formula One and with a move to Marks & Spencer.
But if any sector needs his combination of business-savvy and popular touch it is banking.
What chance of him replacing former Sainsbury's chairman Sir Philip Hampton at Royal Bank of Scotland?