Suppose we build a road. If we build it road and walk away, it will decay into a hazard before long. It will be scoured by wind, rain, and sand. Ultraviolet rays from the sun will break down its molecular structure. The shifting earth beneath will crack and buckle it.

We must maintain what we build, and that requires expense.

Suppose we decide that the road is no longer needed or that it costs more to maintain than it is worth. There is expense to removing what we have built, too.

We cannot just close it and leave it alone. We must divert traffic off of that road to others, which may require some incremental new road construction to make connections. If people have moved into neighborhoods on that road, we must build new routes to connect their homes–or we must relocate them. If there are businesses, we must (somehow) deal with the owners. Once we’ve reduced usage to nothing–which can take years–we must tear up the asphalt or concrete, haul it away (to where?), and restore the land where the road sat.

Let’s consider a smaller case. Consider the humble birdfeeder, a trivial construct. You buy it, hang it, and fill it. The air fills with birdsong and you fill with joy. Of course, the birds eat the feed so you must replenish it. That’s the obvious future cost. Less obvious is that the plastic will degrade and break, and you will eventually replace the whole unit. It may not seem like much to hang the new unit in the old one’s place, but it does cost you time. For the aged or infirm, it may have a capital cost if a handyman is needed. Discarding the old feeder means throwing it in the trash–which you pay to haul away–or recycling–which you or your local government pay for as well.

It would be wise to consider the future cost when you undertake a project to build something. Maintenance, replacement, switching cost, disassembly, and removal… when you account for all of those, perhaps the present value of the project isn’t as appealing as it appeared.