My idea already exists

When an entrepreneur finds that their idea isn't already "taken," there is ostensibly reason to rejoice.

The assumption is that they've happened upon a truly great idea because it is a truly unique idea. However, many of the great ideas and products that now compose modern life were not the first of their kind. The iPhone was not the first phone with an internet connection. It wasn't the first phone that could send and receive email. It wasn't the first phone with a camera. It wasn't even the first phone that could store and play music.

Imagine if Larry Page and Sergey Brin had concluded that there was no place for what became Google because search engines already existed.

Many great ideas are innovations of already-existing ideas.