This is a classic and a must read for everyone that designs for humans. It may seem a bit outdated but the general principles covered still apply today.
If an error is possible, someone will make it. The designer must assume that all possible errors will occur and design so as to minimize the chance of the error in the first place, or its effects once it gets made. Errors should be easy to detect, they should have minimal consequences, and, if possible, their effects should be reversible.
Design influences consumer behavior and a very well designed product will have a competitive edge. This is true in any field.