Interesting. I've read some things about da Vinci and other notable P's that has indicated that this trait is a part of their genius. If da Vinci (just as one example) had been a J and made sure that he pumped out one great piece of work every week or every month (or even every year) - put any type of schedule or "routine" on it that you wish - if he had been on a schedule or routine at all - his works would have ended up being something completely different than what they are. It was the fact that he never thought they were complete (they were always "works in progress") and that he didn't treat these things as "work" - something to be grinded out like a production plant full of conveyor belts - that made his work what it was.
I'm reading a great book right now that talks about how many people "will themselves" to work hard and will themselves to do this and do that. An example would be that you see that you are not doing your best in some area (being respectful to your parents, being the best father or husband you can be, or whatever else it may be). So, recognizing this, you make up your bloody mind to change and you "will yourself" to do better. But, this forging forward on your own becomes oppressive. It becomes a difficult task that we do begrudgingly. "OK honey...I don't want you to get mad and I want to be a good husband, so I'll take out the trash." Meanwhile you're cursing under your breath on your way to the trash can because your heart isn't in it (which is often the case with careers). It's this forging forward and willing yourself that, although productive in a practical sense, causes one to not stop and think. Always forging forward. Always having to complete something. Never stopping to contemplate the true meaning behind something. Why should we treat our spouse better? Why should we respect our parents, no matter how utterly boring they may be?
I'm not saying that J's aren't capable of thinking these things through, but I am saying that P's have more of a tendency to do this. These things are important. To think through and arrive at the meaning behind some action or some thing we ought to do or improve on.
In short, a J may produce, produce, produce. Sell books, bring their work to full production (and lots of it, throughout a lifetime), while a P isn't so concerned about what sells or how he makes a living. He's more concerned about the process. In this book, the author says it is precisely things like worrying if my writing will sell or if people will really like it that kills creativity. Deadlines kill creativity. Just write. Just be creative from the core of who you are. Anxiety, fear of the opinion of others, deadlines, checklists of things to do, and "willing ourselves" to do something kills the creative process. If you sit down with pen in hand to write while thinking "I wonder if this will pay when it's published" or "Oh, how will I pay my bills with this?" then you might as well get up from your chair and go get a 9 to 5 because the writing won't be authentic and it won't be creative. It will be forced and the process will be tiring and feel like "work". If you simply sit down and write and share your gift from the center of who you are (writing from an honest and worry free place), then your writing will absolutely and automatically be good. The 2 things (forging forward by pure effort and the creative process) do not go hand in hand. If you want to make a comfortable, steady living, then get a job doing something that is comfortable and steady. End of story. If you want to be creative, on the other hand, then don't worry too much about things like "comfort" and "steady", but just create - and let things develop in your mind and imagination. Contemplate. Ponder. Take long walks by yourself. Take a drive somewhere. Lay on the couch and let your mind wander. It is in these places where ideas are born. And these types of activities are productive for the P-type. Reading about things that don't help creativity aren't necessarily productive. But, spending time in a place that will aid creative thoughts (if being creative is what you desire) is indeed productive.
May sound fluffy, but I believe it.
Oh, and a side note to this: I sometimes drink caffeine while I write. The author warns against this. She says that by drinking caffeine, you are trying to "speed up" the natural creative process. Your ideas are only at point A and you're trying to get them to point C. Let them develop on their own time. Don't force. Let yourself be a "P"!