I just read an article posted on an Orkut Community. It was speech given by a well known author Chetan Bhagat. In it he talks about how to keep up and nurture the spark in everyone. The Spark he refers to is nothing but Enthusiasm.
3 Things That will Nurture the Spark:
=> Reasonable Goals
=> Balance in Life
=> Don't take life too seriously
4 Things That could put off the Spark:
=> Disappointment
=> Frustration
=> Unfairness
=> Loneliness of purpose (Isolation)