my wife got a patch growing in the back garden after a few failed attempts now we have lots, it's also readily available in supermarkets here in the UK. https://www.bbcgoodfood.com/recipes/rhubarb-crumble
Since when did a customer actual have a solid understanding upfront that was 100% correct. Thats just la la land, and one of reasons for the Agile approach. Iterating after discovery works.