[h2odragon]

Tech debt is lack of infrastructure maintenance.

Metaphor that leaps to my mind: bakery thats in the bread business, but delivers product with trucks... not maintaining the truck fleet would be an equivalent to technical debt; when the trucks fail so does the business, even though the cause might be arguably unrelated with what they do as a business.

Another useful one is "capacity is like a dam, the load is like the lake behind it" and then talk about storms surges and boat wakes slopping water over the edge of it, starting erosion, and then everything falls down catastrophically.