system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Why are airplane windows so small?
gpt
Because the cabin is pressurised - the air pressure inside is kept much higher than the air pressure outside so that you can breathe.

Any holes in the aircraft skin will be put under stress by the pressurisation. Bigger windows means more stress. This would mean that the materials (for both the windows and the aircraft skin) would need to be made thicker to reinforce them. This costs money during manufacture - but it also adds weight, which means you need more fuel (or you can carry fewer passengers/less cargo), so the costs soon start mounting up.