When the plug cannot be used in its functional state as required, then it could be said to have failed. The function of the plug is to connect an electrical appliance to the electrical path in a way that prevents the electrical path formed between user and mains at all state, except when enabled. The plug comes with a set of pins which connect with the socket and are usually so formed that they are tough enough to resist failure, when the plug is dropped or when there are high temperatures, or moisture loss etc. In addition to functionality, they are also supposed to be aesthetic and easy to use and must meet the necessary standards in safety.
Photographic records of the product have to be attached
In this context of manufacturing and functional uses, some of the reasons why the plugs fail are as follows.
Firstly, there could be bad contact heat failure. A plug and its pins must make the necessary connection to the electric socket properly. When the connection is poor, then the plug could get overheated and could fail.
Pugs might be dropped or because of other stress applied on the plug could break.
The plus might be exposed to environmental damage
The materials, such as plastics or other casings used could break.
The plug wiring could be faulty
The material uses in the plugs might show strain of material decomposition over years, etc.