In theory, fly-fishing is a simple sport: Pick a body of water, choose a fly-fishing rod, select your “fly” (or bait), tie a secure knot, cast your line and, hopefully, land a fish on the other end.

A close second would be, “What (or how many) fly patterns do I need to have to be successful most of the time? Those are both valid queries, and ones which reflect the quintessence of fly-fishing. On ...