Final answer:
Uncle Iroh developed the technique of redirecting lightning by studying waterbending arts, allowing Firebenders to safely guide lightning away.
Step-by-step explanation:
Iroh created the technique of lightning redirection by studying the Water Tribe's bending arts. The thought process behind this innovation was recognizing that some philosophies and techniques between the elements could be interchanged or adapted. By observing the flow of water and the emphasis on control and redirection within waterbending, Iroh applied these principles to create a method for Firebenders to safely redirect lightning, a dangerous and advanced form of firebending.