The line I remember best is 'to thine own self be true'. It comes from Shakespeare's Hamlet, and in modern English it simply means be honest with yourself and live according to who you really are.
I first came across it when I was seventeen, studying English literature at a college in Lagos. Our teacher, Mr Okafor, wrote it on the board and asked us to discuss it. In the play, the line is part of some advice an old courtier gives his son, who's about to leave home to study in France. Interestingly, the old man is quite a foolish character, so Shakespeare might have been joking a bit, but the line itself has outlived the joke.
It stayed with me because of what happened a year later. My parents were very keen for me to study medicine, and I applied because it seemed like the respectable choice. But I'd always loved drawing buildings, and I secretly wanted to be an architect. I remember lying awake at night with that line going round in my head. Eventually I found the courage to tell my parents. My father was disappointed at first and didn't speak to me about it for a week, but my mother supported me, and I switched to architecture.
I'm now twenty-nine and work at a design firm in Abuja, and I've never regretted it. The line reminds me that pleasing others at the expense of yourself usually leads to unhappiness. I've even had it printed on a small card that I keep above my desk. When I face a difficult decision, I look at it and ask myself what I really want.