The fly becomes the most important object.
The fly becomes the most important object, since it is, ultimately, the part of the tackle with which the fish is caught. From this point of view, it does not matter that they have spent a fortune on the rod and the same on the other items: An inadequate fly will not attract a single fish.
Although the origin of this style of fishing dates back several centuries, the fundamental idea is still valid: Try to capture the fish, with a lure that simulates or tries to simulate the appearance of the organisms that the fish take as food, insects being an important source of nutrients for them.