There is a saying that “Burma is hell. No one returns from New Guinea.” What made New Guinea one of the worst theaters to campaign in WWII?

I was watching a video with excerpts from a Japanese WWII memoir:

https://m.youtube.com/watch?v=kAn6gU18-HU&pp=ygUPTmV3IGd1aW5lYSB3d2lp

“This video is based on excerpts from “New Guinea, The Island of Death: Human Beings in Extremis,” a WWII memoir by Imperial Japanese Japanese Army veteran Masatsugu Ogawa.”

Why was New Guinea worse than even Burma for troops campaigning there in WWII?