I think it is naive to believe that all plans made will be sucessfully implemented. Nonetheless, it is imperative to plan otherwise the PhD will go on to eternity.
Its important to write everyday and to set a word target. On a good day, I can write 1500 words, only to scrap 500 off the following day. But, hey ho, PhD writing is all about edit, edit, delete, delete, till you get the essence of it and present it nice and crispy.