Many Hardware engineers design their PCBs based on some common knowledge and "rules of thumb."
Rules of thumb are great and seem to work as long as they fit the design case.
In many cases, PCBs designed on rules of thumb do not work, even after a second and third manufacturing spin.
Signal-Integrity simulations, pre and post-layout, must be performed to minimize the risk of a nonworking design.
This video shows some of the reasons why.
Siemens - Hyperlynx SI tools were used for this Test Case.