It can hold you back.  Make you doubt yourself.  Even stop you in your tracks. What is it?

The thought that what you want to do or create has already been done... maybe even by people that are more well known than you.

If you have had this thought then you probably already know that it got a nasty ability to stop you in your tracks from confidently doing what you were feeling the most called and excited to do/create.  Perhaps, leaving you thinking "What's the point?!"