How is it not arrogant to be firm in your belief, even if signals say otherwise? If I believe it is OK not to shower, and everyone around me complains about it, is it not arrogant of me to ignore the signals because "they just don't understand yet"?

I think a much more useful question is whether some arrogance is necessary to succeed. I personally think it is. But we are discussing a post mortem here, and the author is (in my opinion) clearly beating around the bush and using "the time wasn't right" to hide what may be uncomfortable truths.

Is a post mortem valuable if it doesn't address these face first? I am not the one with all the answers here, but what I am used to in mature tech teams is that the uncomfortable parts are usually the most important in any post mortem.

There are plenty of stories about companies that failed because the timing was wrong, and then see another company succeed in their place later on. That doesn't mean failure simply means "the timing was wrong" - you are putting a lot of weight on society adjusting to your belief. Consider that venture capital often invests in hundreds of founders like this, betting that at least one of them wasn't wrong. That's not statistically in your favor.

It is OK (in fact it is valuable) to fail and conclude that your signals may have been wrong. There's a reason some venture capital funds prefer investing in people who have failed before.