Here's an example: I once started writing a book in which the main character was modeled after my first love. I wrote draft after draft, pondered and played with it. From initial concept to completed draft went on for years. Then, in the middle of one rewrite, the man upon whom the novel was based, died. He was young and he died. The impetus that got me to start the story was gone. The me who worked on the book before my friend's death and the me who worked on the book afterward was a different person. The feelings that sparked the book had changed. Likely, they were no longer even relevant.
One of the reasons I wanted to do the 250 words, twice a day, is because I no longer want to lose strings of potentially valuable moments. I've heard that the Muse doesn't come unless you're there to greet her. I want to be available to her more often. Wouldn't it be sad if the Muse came with a gift of the most beautiful story ever written and you weren't there to receive it.