He starts by telling us about the climb itself, but quickly shifts the focus from the event to Hillary's incomplete account about it. Then, he continues to describe the adventure, stopping from time to time, and referring again to Hillary's view. His narration is interrupted with these occasional comments. Apparently, his goal is to provide a more complete and objective account. The point he draws the reader to is that the climb would have been impossible if it weren't for the two of them, and that it is entirely irrelevant who made the first step.
Banquos ghost is who he saw
