You might be playing with PlayStation for a long time but you might not know the meaning of those 4 symbols on your controller - triangle, circle, X and square. Actually there was a lot of thought process that went into selecting them for the very first PlayStation.
The original PlayStation, which launched in the U.S. in 1995, changed the gaming business forever. Teiyu Goto a Japanese product designer started working on the PlayStation in 1993. Once he was done with the basic design of the controller. He started to think about the buttons on it.
In 2010, he explained the meaning behind the symbols and their colours. He said,
Other game companies at the time assigned alphabet letters or colours to the buttons. We wanted something simple to remember, which is why we went with icons or symbols, and I came up with the triangle-circle-X-square combination immediately afterwards. I gave each symbol a meaning and a colour.
He also added,
The triangle refers to viewpoint; I had it represent one's head or direction and made it green. Square refers to a piece of paper; I had it represent menus or documents and made it pink. The circle and X represent 'yes' or 'no' decision-making and I made them red and blue respectively. People thought those colours were mixed up, and I had to reinforce to management that that's what I wanted.
Do you know the original controller design was almost rejected for an odd-looking grip design. But then-Sony-President Norio Ohga somewhat liked the design and chose to go with it.