Most landscapes offer a huge variety of potential options to people, but are constructed in such a way that only a few make sense at any given point. It is much easier for most people to make a series of choices, in which each choice made opens up others logically related to it, rather than being presented with the totality all at once.
In the real world, there are a limited number of ways to move down a street, but moving in one direction or the other opens up other options once a person reaches an intersection. Similarly, airports group their gates and other amenities into terminals, so a person initially chooses the correct terminal, based on their airline, then the correct gate, based on more specific information. Being presented with a list of every gate in the airport initially would make this navigation process more difficult. Grocery stores group items into departments based on their characteristics, so a customer knows to look in a given area depending on what kind of item they want. Within those departments, similar kinds of items are often grouped together on specific shelves or in specialized coolers. A customer doesn’t have to understand the organizing principle, but based on the shape of the cooler, they know what is likely to be there.
In the digital world, designers group similar content or interactions together and disclose information progressively. It is more usable for all the social sharing icons to be in a group together, rather than scattered all over the page. Navigation links and metadata similarly provide more meaning in groups. We also try to design pages with a single primary call to action, so the choices can be limited. It is often possible for a user to do many things, but having a clear best action makes a path clearer to them.