[artdutra04]

While the concepts of constricting the design constraints is a good idea, since it can lead to a better end product (since it requires a lot more thought in the process), not having spares is a bad idea.

What if a computer company like Dell or Apple or Lenovo told their engineers that there would never be any way proclaim a spare battery or hard drive for the laptop they were designing? Even though they might be exceedingly careful with their design, I guarantee you that there will be a small percentage of batteries or hard drives which would fail prematurely, due to any number of reasons which might be beyond the engineer's control.

Stuff fails in the real world, and if you do not design accordingly you won't succeed.