Level designers utilize lot of subtle tricks to draw players in a particular direction or to a particular place, and the majority of their work in this situation is usually pushing players toward the critical path. This is usually a combination of elements like lighting, object placement, landmarks, sight lines, and so on. These kind of level design techniques were actually pioneered by Walt Disney with Disneyland. Those same subtle design elements are physically built into the theme park to guide and direct park goers toward the points of interest.
This is also why most completionists have learned to choose the least accessible, hardest to see, only-visible-from-odd-angles paths first - they’ve learned that you have to “swim against the current” to find the optional content, because most elements will direct you towards the critical path.
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