I wouldn't say heat alone. But it is one of the biggest contenders. However if the device functions according to the manufactor's design, the device shouldn't overheat. The biggest killer is without a doubt electrical damage such as a short circuit. Then there is water (humidity) and dust which is surprising how much damage it can do. Heat of course is also very dangerous but usually heat damage occurs due to the user meddling in. It is rare for a device to overheat by itself..unless the manufactorer is an idiot.