Growing without Erasing

I came across this quote in a book I am reading:

"Humanity does not pass through phases as a train passes through stations: being alive, it has the privilege of always moving yet never leaving anything behind. Whatever we have been, in some sort we still are." (C.S. Lewis, Allegory of Love; qtd. in D. Downing, Planets in Peril 60)

The person is dynamic, ever-developing, but the earlier stages of development are never erased. The person is formed by experiences, obviously. One cannot undo the past. Although we must also allow for the transformation of a person, even a 180 degree change, the past shapes who one is today. The person is shaped by, reacts to, even opposes past experience; thus one's past remains a factor in the formation of the person.