The way The Stanley Parable knows when to grant you the Go Outside achievement is by looking at your last played date on Steam and checking to see if it's at least five years behind whatever your system clock is set to. When you reinstall a game you haven't played for a while, it temporarily overrides the last played date to the present, presumably since Steam's default assumption is that you're installing for the first time, regardless of any prior playtime.





You can probably see how this could cause issues already. If you run the game in this state, you will not earn Go Outside, as the game will not see the correct timestamp for when you have last closed it. To fix this, restart Steam by right clicking on its icon in the system tray, exiting Steam, and then launching it again; your last played date should automatically revert to its correct value.