Design problems factoring in cost.
A problem is to design a product to wear out all at once. Automobiles, for instance. No sense designing a body which would last forever at a great cost, if the engine/drive train will only go 100,000 miles.
Or designing a transmission which will go 300,000 miles if the engine will need replacement after 150,000 miles at a cost exceeding the value of the vehicle with a new engine.
Anyone can design a water pump for a Rolls-Royce. Doesn't matter what it costs. Designing a water pump for a Toyota is a different matter.
Arf