Writing is a form of expression that can be strict or lenient.  Rules and certain structure can be followed or a writer can ignore all of these and completely make it up.  Sometimes while writing for someone else, say a boss or a teacher, it may feel like you're writing with a very large pen.  One that you cannot manage perfectly to create your own writing.  Instead it is so very large that it hinders how you really wish to write.  You are writing yes, but this very large pen is encasing your own preferably small pen and forcing you to follow certain guidelines. 

Occasionally I dislike writing.  Occasionally I think I have great thoughts in my head that I want to share and let others think.  But once I try to transfer them to words and sentences and paper... they seem to lose their meaning.  Occasionally I have a great big thought that is very important to me.  But forming it into a sentence or paragraph is similar to squeezing play-do through a strainer.  Before, this blob of play-do could have been anything, some magnificent, intricate piece of art.  But it cannot remain in its magnificent state after having to be shoved through the strainer.