While taking that cliched photo of the plane wing through the window, have you ever wondered why airplane windows always look the same? Spoiler alert: It has nothing to do with photography.
Real Engineering made a video that explains why airplane windows really need to be round. Basically, it's all about cabin pressure and stress concentration. What happens is, the difference between the internal cabin pressure and the external atmospheric pressure causes the plane to expand a tiny, tiny bit. But, even that tiny bit creates stress.
Back in the day, planes actually had square windows, and that aforementioned stress would concentrate in the four corners of the windows. This ended badly in some instances, creating dangerous cracks in the plane. Since safety is a pretty major concern for anyone flying, well, in the sky, these problems led to investigations, which led to the discovery that round windows handle stress much better.
That's the gist, but listen to the man with the slight accent explain all the details in the video.