You learn more about where the really big fish are. You work in ice-choked rivers, falling time after time, netting giant fish that you have stunned. The more you learn the deeper you're lured into your addiction. There is no satisfaction from fish under 20 inches. Bigger and bigger fish are required to feed your habit.
Bigger fish live in bigger rivers.
You migrate up this big river chasing hatches and spawning runs. Lakes hold even bigger fish. Fish with teeth appear in your nightmares. Barracuda and sharks are with you constantly. The fish in your dreams are leaping out of the blue water, beckoning you to join them.