... that complexity hides deficiencies

"There are two ways of constructing a software design. One way is to make it so
simple that there are obviously no deficiencies. And the other way is to make it
so complicated that there are no obvious deficiencies."

... that they must be involved in implementation

"The designer of a new kind of system must participate fully in the implementation."
"… the designer of a new system must not only be the implementor and the first large-scale user; the designer should also write the first user manual. … If I had not participated fully in all these activities, literally hundreds of improvements would never have been made, because I would never have thought of them or perceived why they were important."