Facebook chief operating officer Sheryl Sandberg, 46, credits her friend Adam Grant for giving her the will to carry on after her husband David Goldberg died aged 47 in May last year.
Goldberg fell off a gym treadmill while on holiday with Sandberg and their two daughters, cracked his head and never regained consciousness.
On Facebook in December last year, Sandberg said Grant had advised her to end each day by writing down three things that she had done that day.
"I tried to do this although some days I had such a hard time thinking of anything I did well that I'd end up listing 'made a cup of tea'," she told Time.
In her foreword to his new book, Originals, she called him "a true friend" who "stepped up and stepped in as only a true friend would" after her husband's sudden death.
Grant, 34, has studied how everyone can feel more fulfilled at work for more than 10 years at the University of Pennsylvania's vaunted Wharton School of Business.
The alumnus of the universities of Harvard and Michigan became Wharton's youngest full professor at age 31 and has been its top-rated teacher for four straight years.
The married father of two also advises mega companies such as Google, Facebook and the United States' Environmental Defense Fund and they, in turn, shower him with wine, jellies and dried fruit.
Born to a lawyer father and teacher mother "with a fix-it gene that I have inherited", he grew up in Detroit very much a non-conformist, playing video games for hours on end and becoming a professional magician after learning sleight of hand as a babysitter to keep his charges quiet.
He was also nicknamed Mr Facts by his playmates because he was faster and more reliable a fact checker than a search engine.
In person, he is "monk-like", says New York Times Magazine writer Susan Dominus, as his hair began falling out in his 20s, a result perhaps of his many childhood allergies to, among other things, blue jeans and chocolate.
Despite being one who "prefers a good book to a party", he is best known for helping others compulsively, be it critiquing a stranger's 300-page draft thesis or advising his students on their career options.