Martin Sorrell, who has done more than most to establish advertising's credibility as a soundly run global industry, declares himself constantly surprised at its collective insecurity.
WPP's chief executive doesn't mean the social defensiveness of the kind that prompted the adman Jacques Seguela to title his autobiography: Don't tell my mother I work in advertising, she thinks I play piano in a brothel.
It's not the accusations of seductive sorcery made against it that bother him so much as advertising's commercial defensiveness resulting from the constant necessity to prove itself to sceptical clients.
The problem is that the industry suffers perpetual inner conflict in its attempts to define what effective advertising actually is. And if its exponents can't reach a consensus, what chance of convincing financial directors and fund managers of its true value?
In an atmosphere of lingering self-doubt, the new Advertising Association-commissioned research is a powerful addition to the industry's defensive firepower.
Although the survey confines itself to the grocery market, its findings have a much broader significance.
Its conclusion is that good products make more money when they are advertised than when they are not.
Surveying the effect of the most sustained-ever assault on premium brands, it's clear that significant ad budgets have enabled most established brands to survive.
The current scenario isn't what many Jeremiahs would have predicted in the 80s when Sainsbury's spearheaded efforts by supermarkets to rid own-labels of their image as cheap alternatives with the purpose of usurping consumer brand loyalty by becoming brands themselves.
Of course, it's impossible to link ad expenditure directly to sales growth.
Creative quality and the efficiency of the media scheduling must play their parts. So too can changes in promotional strategy, heavily advertised but ill-starred product 'improvements' - as Coca-Cola once found to its cost - and even health scares.
None of these factors, though, explain why three-quarters of the named brand leaders in the survey and half the number two brands of 1975 have maintained their places over such an enormous period and despite major incursions by own-labels into nearly all categories.
With the own-label phenomena having peaked in favour of 'everyday low prices', brands look set to sustain dominance of their most important market.
Now, as they switch from defence to attack, they'll need advertising as much as ever.