The inventor of the worldwide web, Sir Tim Berners-Lee, has revealed in an interview that he wishes he had slashed the double-slash, used in all URLs, in the first place.
In an interview with The New York Times, Berners-Lee points out that paper and trees could have been saved if people had not had to write or type out those slashes on paper over the years - "not to mention the human labour and time spent typing those two keystrokes countless millions of times in browser address boxes".
The prefix "//" was a programming convention included in the 1989 paper that led to the birth of the web. But as it turned out, it wasn't really needed.
It's far too late now, of course, and most browsers do the "http://" bit for us.