Criminal Sentence 320: Comma fix

From a blog post:

"I wanted to write fiction, but couldn’t seem to sell it."

This comma is not necessary. Usually, a comma separates two complete sentences before a "but" or "and." So a comma would be necessary if another "I" appeared:

"I wanted to write fiction, but I couldn’t seem to sell it."

I would recommend no comma if there isn't a second "I," but some might say they like the comma because it adds a pause.