So given a Time Turner, I would tell my 21-year-old self that personal happiness lies in knowing that life is not a check-list of acquisition or achievement. Your qualifications, your CV, are not your life, though you will meet many people of my age and older who confuse the two. Life is difficult, and complicated, and beyond anyone’s total control, and the humility to know that will enable you to survive its vicissitudes.

"Books are the quietest and most constant of friends; they are the most accessible and wisest of counselors, and the most patient of teachers."

Under uncertainty, it's better to err on the side of being too aggressive than too passive.