Real origin of 'The Wall'?

This is something that may or may not have been discussed on the forum, but does anyone know the real reason Roger Waters dreamt up the original basis for 'The Wall'?
I only ask 'cos on one hand, according to the Miles documentary written in 1980(?), Waters first had the idea in June 1975 during the US tour:
'During this tour, Roger had the idea of builiding a wall across the stage:
"people con each other that there is no wall between performer and audience, so I thought it would be good to build one out of black polystyrene or something".
However, he didn't follow through on the idea.'
This was when Pink Floyd were starting to play large stadiums - PNE Exhibition Park, Atlanta Baseball Stadium, NJ Roosevelt Stadium, Pittsburgh 3 Rivers Stadium, Milwaukee County Stadium, Montreal Autostade and Hamilton's Wynne Stadium were all played way before the massive shows to support 'Animals' in 1977.

On the other we have a similar theory but based upon that troubled 'In The Flesh' tour, especially the spitting incident at Montreal Olympic Stadium...

Anyone know for sure...1975 or 1977?

Discussed to death.
1977.

So Miles' entry is completely incorrect?

No. Roger may have had the "build a wall" idea in 1975. He mentioned the concept to Bob Ezrin in 1977 in passing, as though he wasn't really considering it seriously. He only started proper work after the spitting incident.

In the Another Brick in the Wall book, it says that roger was feeling isolated and out of place. He wanted to build a wall around himself because he felt that the crowd wasnt worthy of him

One night they were playing a show and simply wasn't connecting with the audience. As a result Roger spit on the crowd. Afterwords he felt very bad about it but still said that it felt like there was a wall of isolation between him and the audience. Soon after he started writing the wall. This was also why the wall was constructed on stage.

Why did that little bastard have to piss Roger off so he spat on him? It's his fault they broke up!

(If anyone here happens to "be" that little bastard, no hard feelings ok?) heh heh.......

I think Roger Waters liked the idea of building the wall on stage in the London concert in 80-81 for the song "Is there anybody out there" On that song the band was behind the wall, but in other songs they were either in front, on top, or sometimes in it. Correct me if im wrong

And didn't the spitting incident occur in an Animals-WYWH tour?

It happened on the 1977 tour, when they played both albums in reverse order.