Every successful book written in the last fifty years (well after the age of Dickens and Dumas, who threw in enough subplots and digressions to make five books live inside one) gives itself one or more limitations that force the writer to innovate. For some of the more obvious limitations, think Stephen King's Dolores Claiborne with its text the spoken narration of the main character, limiting the reader to exactly what she says in an extended police interrogation. Think Dan Brown's three Robert Langdon thrillers which cram in a week's worth of action into about twenty-four hours. Think of every book that gave us a defective narrator, one who is so blinded by anger he cannot see what he's getting himself involved in, or one who has a developmental disability and sees the events of the world in ways that are not immediately obvious to the reader, or one who lives to lie and dissemble and so spins untruth for his benefit or amusement at the reader's expense.
These challenges, self-imposed by the writer, keep the writer engaged and, if the writing and the plot are good, keep the reader reading. "How will this guy get himself out of this mess he's created for himself?" we might ask, expecting to see some form of failure. Writing is only worth reading when when we're balanced along the top ledge of a soaring tower trying to walk a straight line in a gale. That success is only possible where failure stalks but cannot close its teeth around the vivid pulse of the project. We haven't pushed hard enough if the novel couldn't fail; time to reimagine it, rework it, give it some life.
Think of another creative discipline, architecture. In the midwest, most buildings are built on boring flat land, and easily forgotten. The buildings that stick in mind are the ones that had challenges imposed by the natural environment or introduced into the project by the commissioner or the architect. The houses we remember of Frank Lloyd Wright aren't simple boxes. They fight with massive outcroppings of stone or, if they're tethered to a city or a suburb, they flee inward and make the smallest details of window decoration a marvel (in addition to all the other aspects of craft). "This might be a boring place to put a house, but I'll be damned if someone doesn't look out this window and feel inspiration."
Writing is like architecture, needful of major hurdles that could destroy the project, but will seal its success if they are overcome. Good writing should be done without an entire blank page to work on. Limit the vocabulary (think Dr. Seuss). Restrict the point of view. Force your character into a limited range of movement (stranded with a broken-down vehicle). Truncate the time frame. Force yourself to play with only a handful of characters, not an endless casting call. Limit a character's ability to do as he wishes (make him a servant or a man running errands for a sick relative). Hide things from the characters. Lie to the reader and make the reader struggle to unravel the lies. If there is no native challenge in the project you've selected, give yourself a handicap to overcome.