There used to be a situation when I didn't share, and that was only with a particular class of anglers. I refer to authors and writers. In the 60s, a whole lot of new (vast majority were synthetics) materials came out into our fly tying world - trilobal fibers like Antron, plasma coated Mylars, and super hackles like Hoffmans and Metz. In those days, I was in a steep learning curve, and since I was working highly pressured waters like the Cairn's Pool on the Beaverkill, Little Lehigh's Heritage Stretch, Madison Rivers $3 area, South Platte Cheeseman, Frying Pan, etc, many of the very picky trouts (I like 'em that way) would turn up their noses at tried and true patterns - but they would at least look or maybe wiggle a fin at a good presentation. These challenges fired me up into a lot of creativity with tying imitations.
Being a friendly sort, I would chat with like minded anglers on the water, but then I noticed a season or two later, I would see my new unique patterns showing up in the Orvis catalogs and fly fishing magazines. I connected the dots and realized that I might have been the first to show the author my new creation. This happened several times. So afterwards, I became much more guarded when it came to sharing with writers.