When comparing knob and tube wiring with its modern counterpart it is much less resistant to damage. Knob and tube wiring is insulated with cambric or asbestos and is not rated for any exposure to moisture. Some older systems contain insulation with additives that may oxidize the copper wire. Knob and tube can become brittle and bending the wires may cause insulation to crack and peel away.
Knob and tube wiring is often poorly spliced with modern wiring, causing the majority of the issues and fire hazards.
Knob and tube wiring is designed to dissipate heat into the free air. Insulation covering the wiring will disrupt this process. Insulation around K&T wires will cause heat to build up, and this creates a fire hazard. Poorly spliced or maintained knob and tube wiring buried under insulation is both dangerous and difficult in case of fault finding.