I could not find the source, but many years ago I read or watched a story on how instant-pancake-mix had been developed in the seventies or so. It used to be add-water only. It didn’t sell well, but then one of the developers of the mix revealed how they made it a top-seller: just ask people to add an egg. The reasoning was thats not affect the end result, but it makes the buyer feel better about having made something ‘themselves’.
Just like removing the duck.