In all deference to the brilliant Larry David and his HBO series, I suggest we don't curb our enthusiasm. It is too rare a commodity and one often scoffed at as ingenuous or naive. Of course there are some individuals who do seem to overdue it–but for the most part, it is in short supply.
It is interesting to note that at one time the term was somewhat derogatory, referring to a vain self- promoting sense of spiritual superiority. But its original Greek etymology is literally from etheos meaning god possessed.
Enthusiastic individuals are driven by a sense of optimism. They are exuberant. They are not self-conscious about their approach to life and are often oblivious to the condescending opinions of others. They seem immune to the cynicism and negativity that permeates society in general.
At times we may regard them as annoying because they seem to savor what may appear to the rest of us to be quite ordinary and mundane. In fact on some level we wish we could see the world through their eyes.
So let us embrace enthusiasm. But if you're not quite ready, at least let's not curb it in others.