What is enthusiasm? Enthusiasm means to be connected to God within. When you are with your source, you can only be enthusiastic. Apathy is when you are away from the source of life. You cannot be but enthusiastic when your mind is totally in the present moment.
You should know that dispassion is not apathy. It is simply a broader perspective of reality. Dispassion is moving towards the source. Dispassion simply means the way back home. It is the journey towards the source, which is a reservoir of enthusiasm.
When dispassion and enthusiasm co-exist, that is the secret of perennial enthusiasm and profound dispassion. Though they appear to be opposite, they are actually complementary.