Du Plessis formerly ran his own research company, Impact Information, in South Africa.
Compiling research performed by du Plessis and Millward Brown, "The Advertised Mind" theorizes that the strongest factor in successful marketing is whether an advertisement creates an emotional response in its target audience.
du Plessis bases his conclusions on recent discoveries in neuroscience—particularly the limbic system—which suggest that emotion establishes a firm memory of an advertisement and predisposes consumers to buy the brand that is being advertised.
du Plessis also refers to Adtrack's database of responses to over 30,000 TV commercials, and explores how this paradigm shift can maximize return on advertising spend.
Du Plessis also offers some insight in his book on the ways in which emotions, moods, personality, and culture impact our brand decisions.