How long can you fake it?

I was out with a friend today and we were talking about life. Yup... one of those conversation :p I was telling him about some of my work when he said, "My God, you really believe in what you do!"

Of course I believe in what I do. I'd never do anything I don't believe in. Because if you don't, you'll have to fake it and then the only question that remains is how long can you fake it?