If you continue to defy the Narrator in the HD remake, you'll come across two doors, red and blue, and the Narrator instructs Stanley to enter the red door. If you notice, next to the red door is a red hand truck- visual symbolism that by going in the red door, you're going back to being "carted around" by the narrator.
One of the only consistent descriptions that the narrator gives Stanley is that his job is pushing buttons, and that is essentially the only thing that you can do as Stanley, you push buttons to go up or down lifts, you push buttons to open doors, you push buttons to give feedback, to turn off machines, and to save babies from fires. There is only one real instance in which you can make a choice which doesn't involve pushing a button, and that's when you pull the telephone plug out, at which point the narrator realises that you can't be Stanley and instead must be a real person.
Naturally, you do that by pointing Stanley at the plug and pushing your action button.
The number "8" is a number that is repeated often, such as in the Demo and, in the Real Person ending, the presentation claims that doctors recommend making 8 choices a day. Why Eight? Because eight is the Infinity Symbol on its side, and it has no beginning or end. The theme that the game has no ending is very prominent in several of the endings (Such as the Museum ending when the second Narrator says the two will be in conflict forever because the game restarts) and on the loading screen the text "THE END IS NEVER THE END IS NEVER THE END etc." The game and Stanley's manipulation by the narrator is a never ending cycle, thus why the most important number is the one without beginning or end. 8.
However, on the Reddit AMA, Word of God states that they chose the number 8 because "Why not? Do you have a better number?"
From the HD Remix Demo: in the emotion booth room, there's only two booths you can enter, and most of the others are switched off. Behind the two open booths, in the back row, there's a single booth that's labelled and lit: Fear.