There are hundreds of different kinds of mayflies that hatch at different times on different bodies of water; and there are virtually hundreds of patterns that imitate those mayflies, but most mayflies can be represented by one of a handful of patterns generic enough to get the job done.
Blue Wing Olives, for one, can be represented with the same tie, only in different sizes ranging from 12 – 22 …smaller if you can tie them. Adams and Borchers are generic enough to cover most of the hatches beginning with the Hendrickson hatch.
Brown Drakes and Iso’s can share a common pattern and of course so can hex. Terrestrials are in that category too. Hoppers, for example have dozens of patterns, but I’m partial to Joe’s hopper in various sizes in a few different body colors.
The point is, trying to tie every pattern you see fills up a lot of boxes, (I’ve been guilty of doing this) but only a few will produce consistently. I think any hook with feathers and fur on it will at one time or another catch a fish, so it gets down to favorites with a lot of patterns getting seldom used.
I think Jerry Regan put it best when he said, “My grandmother told me, in order to catch fish, you have to keep the fly on the water.”
TD