What he said.

"One is none and two is one" is not meant to be taken literally as math, nor is it an untruth. Of course one is one and not none. It's a principle of preparedness that encourages us to have backup for critical items. One is better than none, but that one can fail you, quite easily sometimes. Having redundancy in some places just makes sense.

Further, it encourages us to carry two different methods to achieve each goal. Lighters rock, for example. They're excellent fire starting tools, but if your fingers are frozen or you run out of fuel, you might have better luck with a ferro rod. Or vice versa. A ferro rod will give you 1,000 fires even if it gets wet, but maybe you need a more instantaneous fire like a Zippo can provide be cause you fell in the icy creek and don't have time to spend with your tinder.

If you don't agree with the theory, that's fine too. Some of us overdo it sometimes, and I could well be the president of the club, but better IMO to have it and not need it than the other way around. The only person that has to carry my pack is me and it's up to me to prioritize my needs. I ask for feedback, looking for new ideas to save weight/space and to identify gaps, and it's always an interesting process. Some people say I have too much fire and not enough fire power, as an example, or not enough electronics but too many lights. I listen, think, and adjust as I see fit. In the end, it's up to me. If you want to carry only singles of everything, go for it. We'll hopefully never need it anyway, but my redundancies make me feel better and I'm happy to carry them, practice with them, and try to figure out how to improve on them.