Brian Marick (see link on side nav) has been blogging about new metaphors for technical debt. He used "fertile assets", a gardening metaphor, which I like. If you don't amend the soil and plant your seeds at the right depth and weed thoughtfully, you won't get a good harvest. You might garden rather lazily like me and use ground covers and minimum tillage, but those are still good practices and produce good results. But if you let all the weeds grow up, it might be hard to remove them without damaging the good plants. Just like code that's hard to change if you don't have automated tests to tell you something got damaged.
I like Brian's metaphor, but to me, it's too positive. If we don't protect our code with tests, and don't refactor continually, and just hack in code changes without thinking, we won't just have a bad harvest, we might ruin the soil so it can't grow anything again.
I think technical debt is more like global warming. Lots of people claim it's just a myth and that we can ignore it. If I, as a tester, try to use good practices, but the programmers don't, it's like Denmark being green but not China. If everyone collaborates on a solution, emissions will go down quicker, and we will all breathe easier.
But, since global warming is a politically charged subject, it will get people arguing about that instead of thinking about how to make teams understand how shortcuts, poor design and lack of automation will grow an ever-larger burden for them to carry.
I'm now working on a metaphor that involves donkeys, perhaps log skidding. Recently my friends cut some small trees and branches near their creek bottom to make room for a bridge. We used the mini donkeys to haul the wood and brush over to the cabin's woodpile. If we tried to put too many logs in the bundle, or tied them so they dragged too much in the dirt, the donkeys had trouble pulling them up the hill. If we didn't take the time to tie them together well, they fell off. But when we took enough time to prepare optimally-sized, securely-tied, drag-dynamic bundles, we could make quick trips, and the woodpile grew fast. A little experimentation taught us that cutting corners didn't pay off.