This explanation applies to tiny electronic parts and not necessarily large structures. The main objective is to get as far away from any structural resonance points as you can. Low frequency resonances are not bad from the perspective of damage to electronic parts because low frequency equals low energy, but on the downside, low frequency equals large amplitude. High frequency resonances sometimes are of such low amplitude that you can't see the motion, but you can feel it with your fingers. The thing to remember is that high frequency equals high energy and that is a bad thing. Because this is closer to the natural frequency of tiny component assemblies, they are more likely to break when subject to such an environment. Making something structurally stiff might seem like the smart way to go, and it probably is where structures are concerned, but when it comes to tiny vibration sensitive parts, the objective is to decouple them from the source of vibration by reducing stiffness. Another approach is to use some sort of vibration isolators. For small parts, it could be something as simple as a small soft pad made from open-cell foam. Closed-cell foam is usually too stiff. In addition, mass can be added on the electronics side of the isolator to lower the overall resonant frequency of the electronics.
