ELI5 Circular Windows - why don't planes and ships have square windows?

Why did the De Havilland Comet aircraft lead to a critical design decision? Why do planes and ships have circular windows instead of square ones? Why do airplanes have more windows than seat rows?   ... We explain like i'm five!   Thank you to the r/explainlikeimfive community as always and in particular the following users whose questions and comments formed the basis of this discussion: lilmamameows, deep_sea2, crazykentucky, majasshole, peach-fuzz1, hiteshhedwig, concise_pirate & mjmurcott Wikipedia reference: https://en.wikipedia.org/wiki/De_Havilland_Comet To the ELI5 community that has supported us so far, thanks for all your feedback and comments. Join us on Twitter: https://www.twitter.com/eli5ThePodcast/ or send us an e-mail: [email protected]