Scientists are trying to come up with theories to link up the forces in physics. One is called the Grand Unification Theory, another is called the Theory of Everything. Others may be looking at other causes and effects, at things that may be linked to changes to eco systems, global warming, the weather, the ozone layer, all sorts of different systems like economies and societies. Even in anthropology there is what they call "the missing link".
In the offline and online worlds, there is the game / theory of six degrees of separation between people. Though maybe there are less degrees between some people on LiveJournal via friend's lists. That is how I find other people's journals, by looking at entries and replies to them, or looking at their flists. [I Wonder how many LJ writers have more than the max number of friends on their lists.]
The Domino or Butterfly effects, where small changes affect slightly bigger changes and linked in turned to more bigger changes in a system like weather or financial markets. They are linked together by a knock on effect, maybe chance or circumstance.
There are chains of things, such as chain of command, where orders and information are passed from one level to another within a group. The supply chain of materials, inventory and products. The food chain of lower / smaller life forms being consumed by higher bigger ones.
Disease in epidemic outbreaks, might follow trails spread out from a source. So people have to try and contain the outbreak and follow the paths back to it's origin. Computer (adventure) games, where you need to find x, give it to person a, to get thing y for person b for object z etc. are too linear if all problems are linked together one after the other.
The internet was first designed to be linked in a certain way, so that knocking out some parts of the network would not affect the overall working of it. The packets of data would take a different route around the holes in the network to reach their destination. In one sense, could it be that everyone with access to the internet is theoretically connected to anyone else online at the same time? Almost every internet connection could reach almost any other one in the whole wide world, access privileges notwithstanding. Some people don't want to be connected physically at all, and instead want wireless communications to link their network.
The infinity symbols (I guess there are probably more than one), where the end is connected back to it's beginning forming a loop or sorts. When things come back full circle, a conclusion leading back to beginning of story, if possible, or a journey returning to the start. Some stars are linked in the minds of astrologers or astronomers to form constellations, a little like a dot to dot puzzle.
These days with gmail invites, where one person who signs up can get 6 invites to send to others, and they in turn will eventually get 6 invites themselves, and so on, until everyone on the net has one, seem to be linking people in a way. In a sense they are like a viral or chain letter, pyramid scheme, though everyone gets something out of it.
So that's all, a mostly random post with not much to actually link the text together, except that I've just put them here. Was trying to group together things that I think are linked in some way to something else.