[GeeTwo]

While there are only six actual degrees of freedom, looking only at motion directly along each one is not enough. You need to consider all of the diagonal possibilities as well. I recall seeing a documentary about a building in NYC that had some cantilevered sections. Engineers wind-tunnel tested models for north, south, east, and west winds. It passed, and was built. After it was built, it behaved as expected in north, south, east, and west winds. When the first nor'easter blew in, the building swayed dangerously, and they had to retrofit structure into a working office building by night to prevent a "domino effect" of falling buildings. When it comes to safety, consider the "in between" cases.