It so happens that every bridge is also a wall but not every wall is a bridge. We tend to think of bridges as bringing people together, but they also end up walling off (at least in part) communication along the body that separates two people or places. That which we use to facilitate communication between two areas will also inhibit other means of communication between them. If one builds a canal, one cuts off land communication between areas that were once connected by land but now have an artificial body of water between them, and if one builds a bridge over a river or a causeway over a narrow strait, one inhibits the sea or river transportation that used to go along that body of water that is now blocked off by it being connected to land. We do not tend to think of that because humanity tends to think of what is gained by doing something and not what is lost. Opportunity costs are something that we seldom ponder, but sunk costs are in our minds and influence our behavior even if we can no longer do anything about them.
Is it preferable to build a bridge or to build a canal? A bridge or causeway puts land where there was once water, cutting off a body of water to make land communication and travel between two places easier. On the other hand, a canal puts water where there was once land, cutting a body of land into islands separated from each other so as to make water transportation easier. Much depends on whether one is trying to transport goods or people. The slow speed of sea transportation relative to land (and especially air) makes it difficult to transfer people given the sort of interests we have in speed. Where cruises were once a feasible means of transporting people between continents, we are far too impatient for that these days and tend to travel by air when we cannot travel by land. Yet the transport of goods is vastly less expensive by sea than by land and much less expensive by land than by air, and so we still transport a lot of goods by sea because our need for them is less urgent than our need for speed in our own personal transportation. Those who are in a hurry pay for that hurry in a big way by the costs of air shipping.
There are sometimes attempts made at compromising between building a bridge over a body of water and keeping it free for river transport by drawbridges, but what these do is block of either the river or the land transportation depending on whether the bridge is up or down. Freedom to travel in one direction blocks off transportation in other direction, and vice versa. Life is full of these choices. Do we develop our country internally and seek to protect patriotic industry or do we develop externally and subject ourselves to the ups and downs of neo-colonial relationship with financiers and merchants? Do we seek to encourage politeness and civility among ourselves and others or do we cultivate a radical devotion to honesty and candor that may reveal unpleasant thoughts and feelings about others that may be difficult to accept and handle? One route forecloses the other. And even where, we can break through the two-dimensional reality that seaborne and land transportation entail, we find other constraints that make space at a premium whether we travel in the air or below the sea, and thus make it impossible to do some things or at least way more expensive to do them because of those constraints. We are always constrained, no matter which way we turn. The universe we live in forces us to make decisions and to accept the repercussions of the choices we have made. Every gain is coupled by a loss, and correspondingly every loss comes with the opportunity of gain, even if it is a gain that may be hard to initially recognize depending on where our attention has been focused. And life goes on, based on the choices we and others have made.