It's a practice Sandberg began after the death of her husband, SurveyMonkey chief executive Dave Goldberg, earlier this year.
"Some days it was hard – made tea," she told a packed audience at the Grace Hopper Celebration of Women in Computing of one entry.
Instead of focusing on what went wrong, Sandberg said she now ended the day by focusing on the successes.
In 2013 Sandberg published the best-selling book "Lean In," which encouraged women to take a seat at the corporate table rather than shying away from full participation.
"Confidence and leadership are muscles. You learn to use them or lose them," she told the Houston conference on Thursday.
She also encouraged attendees to stay in tech, saying jobs in the industry were great: well-paid, flexible and high-impact.