While there are a few things that I do think top enthusiasm in life (love, family, faith), I have to agree with Tennessee Williams that enthusiasm is way up there.
I used to hear that quote from Emerson that "nothing great was ever achieved without enthusiasm" and I'm only beginning to understand how true it is.
Do you approach each day or each task with enthusiasm? For a long time, I certainly didn't...but now I'm so grateful to have a job I love and a daily routine I feel excited about.
Who knows? Maybe injecting a little enthusiasm into your life will have a positive effect!