For all the controversy surrounding John Broadus Watson and his famous Little Albert study, it was what was happening behind the scenes at the time that ultimately cost him his position at John Hopkins University. During the winter of 1919-1920, all of the work that he did with eleven-month Little Albert was conducted with the help of his bright young graduate student, Rosalie Rayner. Their collaboration continued for months and he spent more and more time away from home and in his assistant's company. Whatever suspicions that Watson's wife had of what was happening between her husband and Rayner seemed confirmed when she found a passionate note in his coat pocket. The note was from Rosalie Rayner to her husband and Mary Watson had good cause to question her husband's fidelity (he had strayed before, after all).
Knowing that she needed more evidence, Mary took advantage of a dinner invitation at the home of Rosalie's parents to investigate further. After pretending that she had a headache and needed to lie down for a while, she sneaked into Rosalie's bedroom and found love letters that John Watson had written to Rosalie. The letters were graphic enough to give her all the proof that she needed. Mary Watson confronted her husband and threatening to ruin his career if he didn't end his relationship with Rosalie immediately. When he refused, she decided on a very public divorce.
Not only did the divorce proceedings become front-page news in Baltimore, but copies of the love letters were sent to the president of the university, Frank Goodnow (whether the letters were sent by Mary herself or her brother isn't known). Even today, an affair between a faculty member and a graduate student is considered improper but back then it was unforgivable. Goodnow demanded his resignation and John Watson, up to then a rising light in psychology, would never work as an academic again. Once his divorce from Mary was finalized, John and Rosalie were married in 1921 and they would eventually have two sons together.
Although his academic career was over, John Broadus Watson was still very much a psychologist and the behaviourist school that he had spearheaded was just beginning to gain force. Bitter over the lack of support from the university and his fellow psychologists, John and Rosalie moved to New York City where he used the contacts developed by fellow psychologist E.B. Titchener to become resident psychologist for the J. Walter Thompson advertising agency. Still one of the largest advertising agencies in the United States, the Thompson Agency (now known as JWT) provided Watson with an opportunity to merge psychology and advertising to create new and innovative new campaigns to sell a wide variety of products. During his time with the agency, Watson developed some of the most successful campaigns in the agency's history including ads for Pond's Cold Creams (he obtained testimonials from the Queens of Spain and Romania praising the product), Johnson and Johnson baby powder, and Maxwell House instant coffee. Watson is now considered to be one of the pioneers of modern advertising and continued to draw an enormous salary even at the height of the Depression. He and Rosalie settled down on a large hobby farm in Connecticut and he devoted his time puttering on the farm when he wasn't working in New York.
Along with his extremely lucrative advertising work, John Watson also became an author of popular books and magazine articles on psychology. Most of his books and articles focused on behaviourism, particularly in using behavioural principles to raise children. Using the slogan of "not more babies but better brought up babies", he also became famous (or infamous depending on your perspective) for his outspoke support of nurture over nature in child-rearing. In his classic book, Behaviorism, he provided his famous "Twelve Infants" quotation:
Give me a dozen healthy infants, well-formed, and my own specified world to bring them up in and I'll guarantee to take any one at random and train him to become any type of specialist I might select – doctor, lawyer, artist, merchant-chief and, yes, even beggar-man and thief, regardless of his talents, penchants, tendencies, abilities, vocations, and race of his ancestors. I am going beyond my facts and I admit it, but so have the advocates of the contrary and they have been doing it for many thousands of years.
The last sentence is often omitted from the quote giving Watson a more radical reputation as a behaviourist than he likely deserves. Still, his theories about child development must have seemed radical enough at the time. Though politically conservative, he considered behaviourism to be the ideal way to mold a child's personality and to counteract the dominant hereditarian views of the time (racial theories inspired by Francis Galton and other eugenics writers were still very much in favour). In his 1928 book, Psychological Care of Infant and Child (co-written with Rosalie Rayner), Watson insisted that children be treated as young adults and that mothers refrain from providing too much love and affection to their children. Since society as a whole didn't provide adults with unconditional love and support, parents needed to prepare children for their place in society by not giving them unrealistic expectations. He also advised against letting children sit on their parents' lap or otherwise encouraging emotional dependence. The book became extremely popular and American parents regarded it as the de facto reference manual for child-rearing for decades afterward.
By all accounts, he was a stern and unemotional father who had no difficulty putting his own behaviourist theories of upbringing into practice. His two children by his first wife included a daughter, Polly and a son, John, who were both plagued with lifelong emotional and medical issues. Whether that was due to Watson's unemotional parenting or the scandalous breakup of his marriage to Mary seems open to question.