E-mails don’t reach you in envelopes. However, the desktop icon of your e'mail software looks quite like the envelopes humans once used to send letters. This illustrates how every innovation must pass through a first stage in which the new effect is secured by the old. A designers' trick to make the new accessible through the known. This is called a horseless carriage. A concept that origins from the first cars: they looked like horse carriages but without the horses.
From the Analogue vs Digital Memory Game