Clarifications

 It turns out that it is perfectly possible to hand knit (with no knitting sheath) with flat tipped "knitting pins".

It takes learning the knack, and being careful about the orientation of stitches, but that said, there is no problem either in knitting or purling. On the other hand, hand held needles do not allow knitting as fast or as long as when used with a knitting sheath.

When I said blunt needles were not suited for hand-held knitting, I was working with very fine, very tightly knit fabrics, and it was the tightness of the fabric that caused the problems, not using blunt needles, per se.

For the last day or so, I have been using flat tipped, 2.3 mm needles to knit 4-ply, worsted weight yarn at 6 spi and 6-ply gansey yarn (1,000 ypp) at 7 spi. Neither are weather proof fabrics, but they are nice firm fabrics. These fabrics could be fulled and oiled to be water repellent. However, once they did get wet they would be a pain to dry, and would not be comfortable to wear within 15 minutes of putting on, like a true weatherproof fabric where a thin layer of wool next to the body dries almost instantly, and protects the skin from the still wet and cold bulk of the fabric.  Gansey knit, weatherproof wool fabrics are special, they require effort to knit, but they are special.

Moreover, since the knitting motions using blunt needles can be much smaller than is possible with pointed needles, the knitting can be faster, with less stress on the hands considering the knitting speed and type of fabric. Early on, I was told by champion speed knitters that more pointed needles could knit faster. Those champions specialized in a narrow segment of the craft, and had a very narrow view. The key to fast knitting is small motions, and no extra motions. Yes, I use my right index finger as a shuttle to loop yarn, but the motion is only a few millimeters. The flat tip of my working needle only protrudes a few millimeters from the working stitch, so all my knitting motions are very small, and can be made quickly.  If I am using sock needles, most people will not notice I am knitting. (These days I mostly knit socks on 12" needles.) If we are talking, I look at them, and not my knitting.  If I am out and about, I watch for people and particularly kids moving about.  I can watch a movie, and not look at my knitting. Some of my knitting sheaths have all the dimensions required to knit various kinds of socks that fit me notched into them. I have "storyboards" with notches for the dimensions needed to knit socks other other people.  

The key to getting a lot of knitting done is ergonomic knitting. Let the big muscles, and tendons of the arms and shoulders do the work. Use the leverage of the knitting needles to put less stress on the knitter's body. And, I like to use the spring of steel needles to do part of the work of knitting. 18", 2.3 mm blunt spring-steel, "needles" with a good knitting sheath on a heavy leather belt worn over a stout apron or bib overalls is the most productive hand knitting gear that I know.  (Actually, these days, socks are knit on 3+1, 12" long needles.) The leather belt and apron stabilize the knitting sheath, and make it a more powerful tool.  This has been a major epiphany over the last few months. 

And, knitting is athletic activity. You cannot sit around for months, then expect to go out, run a marathon and not be sore. You need to train for knitting just as you would train running. Yes you will be training different muscles and tendons, but the idea of a gradual build up in duration and intensity of the exercise holds.