What you describe is not what I've experienced with debt. Usually it is a conflict where short term goals and long term goals are at odds with each other. Using your bridge analogy, its more like "We only need an infantry bridge right now, but we know that in a year we need to support tanks". Well we can either spend $2m to build the tank bridge now, or we can spend $1m today for the infantry, but in a year you'll have to spend another $1.5m to make modifications to support tanks.

The debt there is knowing that "we will spend $500k more doing it this way (interest) but we will benefit in the meantime".

There are other factors too that make the true cost of the debt higher. For instance less flexibility as requirements change. I often find myself saying "this would be an easy change if we had initially built it in the more extensible way, but at the time you didn't need/want for extensibility so now your easy feature is actually a large refactor"