You could be picking up that ripe avocado from the produce section (even though we all know it belongs by the fruit) and *bam* a character just walks into your mind or a paper blossoms in front of you. Yes, the character could like an avocado, has green skin or hair, or is just misunderstood by society, and, sure, that paper could be about the hidden qualities of the vegetable/fruit industry or why certain fruits are green, but your new idea could be completely unrelated, too. And that's okay. That's the beauty of that idea, that spark, that creative energy inside of you.
Go with it. Buy the avocado, get home, and put pen to paper or fingers to keyboard and write. Simply write it out, unhindered by your inner critique, get that first draft down and, after everything is said and done, go back and edit.
And, if you ever need a second pair of eyes, ask an editor. I know of a good one in town.