"My convictions have validity for me because I have experimented with the compounds of ideas of others in the laboratory of my mind. And I've tested the results in the living out of my life. At twenty-one, I had drawn an abstract map based on the evidence of others. At sixty, I have accumulated a practical guide grounded in my own experience. At twenty-one, I could discuss transportation theory with authority. At sixty, I know which bus to catch to go where, what the fare is, and how to get back home again. It is not my bus, but I know how to use it."