In one sentence: Excel seems magic because when you copy and paste cells the references change to still work, but you can understand in less than a minute exactly how and why that happens if you learn R1C1.
In two more sentences: Specifically if you're in cell A1 and you enter =B1 what is actually stored is =RC[1] (same row, one column more relative to this cell). So if you copy that into cell H50 it will still be RC[1] and now evaluate to I50.
https://answers.microsoft.com/en-us/msoffice/forum/msoffice_...
Ed: ok, apparently the video starts with r1c1 - so I guess I've found my elevator pitch...