In the case of the original post, he is talking about light weight road bikes with equally small light motors. If pushed hard, they don't have the headroom offered by the mid motors in less exquisite bikes. Then when you bring hub motors into the picture, they are even larger and can be loafed along, rarely tapping into their power. Many of us have more motor than we ever use, and in those situations, they won't fail. Still, if you run them hard, the insulation on the motor cables melts and motor windings turn black, if the nylon gears haven't already turned soft and shredded,