Unable to assign a task to myself in Docs...

Unable to assign a task to myself in Docs...

I was working on a document, and could not finish updating everything I needed when I closed the Doc.  I started to leave a "comment" for myself to remember what I needed to update, and then remembered I could assign a task to a doc... Unfortunately, when I try I get a message that says I cannot assign task to myself... 

I believe I was able to do this in the past, but I could be incorrect. Why can I not assign a task to myself on a doc? I want to setup times to get back to things for specific documents, but it is not letting me... Don't understand.