You Cannot Test Quality Into A Product; You Must Design And Build It In!! ─ Law #26
The best way to achieve good quality is with a good design.
All the testing in the world will not improve the basic quality of the design.
Testing can give a false sense of security if the basic design is inherently marginal. Be wary of a design fix rather than a design change, as a fix may create other problems.
A customer will be reminded of a bad design and bad performance forever.