Poetry is indeed an expression of the way a person feels. As such, there is no set rule on how it should be done even through there are different types.
Writing a poem is not bound by any rules because it is a personal work that is based on personal feelings and as such a person is allowed to express that feeling however way they want to. It is up to the reader to decide if they want to read that poem or not but they cannot impress upon the poet what to write.
