What would you call someone who is extremely independent and thinks that they can do everything on their own, but in reality they are getting swamped and cannot handle the pressure without help. Not a loner, just likes to handle things by themselves without getting anyone else involved. Is there such a word or phrase?
You could say that person:
To try to do more than you are able to do.
Don't bite off more than you can chew. Let someone else organize the party.