Many people (including me mostly) don't understand why their eyes feel something as "good-looking" or "beauty". It boils down to symmetry being a big part of it, and sometimes symmetry creates working solution. A bridge being the perfect example for that since you need to balance the weight between both sides of the bridge it's easy to get this while also "looking good". But I believe symmetry is not the only thing our brain accounts to beauty. I would love to know more about that topic.