Jane Fraser, the British-born head of Citigroup's consumer and commercial bank, shares a lesson she's learned from her 13-year-old son that has helped her adapt to her new role. She also talks about making a scary transition to a job overseeing U.S. mortgages and training yourself to overcome fear and take on "stretch assignments" at work. "You just have to be 'all in' — mind, heart, guts, hours," says Fraser, the No. 1 Woman to Watch, in her speech at the Most Powerful Women in Banking and Finance awards gala.