The diagrams of the spectrum bands are wild for me (coming from the RF world) - in that world, a 2GHz channel that I'd used in some systems was considered ridiculously huge, but here in fibre the 'small' channels are 50GHz!

People really don't get the enormity of the difference - when there were policy debates in my country about rolling our new fixed line infrastructure there were literally people saying "but won't all homes and businesses just be able to use wireless in the future?"