Beyond the expense and time, mistakes can also be very dangerous. I take a lot of pride in designing industrial machines that are not only effective at their task, but safe to build and operate. The products that I've had a hand in are touched by a lot of people, and it's my responsibility to make sure that the energies being transformed by the machine are not unleashed in ways that are harmful to people. Laziness or lack of care on my part will get people hurt.