Any electronic or mechanical devise is designed to operate in a safe operating range .... You car will likely operate fine going 65 mph on a 55 mph road but the ability of you and the car to operate much higher is limited by your reaction times, sight distance, tire friction, stopping distances etc. Same thing. In shrinking the die down to a reasonable size, the individual circuits can safely operate within know voltage, amperage and temperature limits. Exceed them a bit and all will be well due to designed on safety factors.....some due to the vagaries of manufacturing will do better than others. Keep pushing and they either generate too much heat for the cooling system to handle or electrons start to jump from one circuit to another.
This will result in instabilities, thermal throttling and if pushed too far even damage.