There are a bunch of inaccurate stereotypes floating around about J/P, and they're just plain wrong. I don't know where they came from, I don't know why they persist, but they're false, inaccurate, and unreliable. (Have I stated that strongly enough?!) People forget about all the other letters, they forget about the theory, they forget it's about a personality pattern not about traits -- and they hone in on two letters: J & P, as if the mysteries of the world can be solved with just these two letters. Argh!
The first stereotype is the notion that J's are always on time, and P's are always late. IT'S NOT TRUE!
Two J's live together in my household, and we're often late for appointments. In fact, the standing joke around here is that "J" stands for "Just One More Thing!" -- meaning we invariably try to accomplish one additional thing before we charge out the door. We do not have a reputation for reliably being on time (ask my ISTJ sister!).
In contrast, I've met P's who arrive at the airport several hours ahead of their flights, and arrive well in advance of any meetings. (Interestingly, one P admitted to me that he arrived early as a way of compensation for an acknowledged tendency to be late. Viva le compensation!)
The point is, if you're using a stopwatch to distinguish P and J, you are wasting your time.
Another myth is about Js being tidy and Ps being messy. Whoa again!
The messiest house I've ever seen in my life belonged to an ESFJ. It looked like a garage sale gone mad -- with a layer of dust everywhere to boot! The "J" house I live in with my husband looks like a tornado went through it.
Do you know who's probably the tidiest person I know? My ISTP dad, of course. (Notice the last letter, willya?) I also spent 8 years living with an ENFP -- and he would win the neatness award long before I would even be eligible. So saying J's are tidy and P's are messy is FALSE!
Then there's the added problem of people who try to figure out whether they are J or P based on these same criteria! Well, as the Mafiosos say, "fuhgettabouttit!"
Linda Berens has said that NJ often looks like P.
And boy is that true in my NJ house. What's interesting is that my husband and I score equally on the questions of early-starting and pressure-prompted -- because we do both! Since we both possess the Chart-the-Course interaction style, we tend to put just enough energy into an event early on in the process to figure out what must be done to arrive at the goal point. But then we forget about the whole matter until we're "pressure-prompted" to actually set the wheels in motion for the event. Invariably, we cut the margin too finely, and quality of life can be rather questionable until the event has ended.
There are other stereotypes around J/P -- you probably know what they are. I've heard that "Js are determined and energetic while Ps are unmotivated wimps." Whuh?! Where is that written, I wonder? Does that describe a healthy attribute of Type, as Isabel Myers intended? I don't THINK so!! And it's about as true as saying men are from Mars and women are from Venus.
Dr. Berens says that if we spend too much time talking about J, before long we're really talking about SJ (extreme SJ!)... and if we spend too much time talking about P, we're really talking about NP (extreme NP!). So it's not good to single out and focus on J/P alone for drawing lots of Type conclusions.
Whenever I see conversation deteriorate to the point that J and P are the only letters I'm hearing, then I know we're not talking type theory anymore -- we're talking bias and stereotype, and that means we don't know enough about type theory overall to keep the conversation going properly. I don't have patience for that, and I believe it's ignorant and inappropriate.
The bottom line is that you can't point at that last letter and make a boatload of assumptions about it -- because whatever you assume will prove untrue for some portion of Earth's population. So don't do it.