Hi topdog, The actual reason is that when the filament is cold the electrical resistance is low and at switch on time the current taken will be very high for a few milliseconds until the filament heats up and its resistance increases, this places very large stresses on the wire which is most likely to break at this time. Note also that if the voltage on the lamp is even slightly higher than its rated voltage the life will be reduced by a lot, if you live close to the transformer in your area this might be a problem.