The Wrong ROM
ROMs are memory read at high speed that are not capable of being changed by program instructions. These ROMs bring all kinds of functionality. However, in some cases, the wrong one will ruin your phone. Flashing an incorrect ROM could even render the cell radio dead. There are ROMs made for your device; find those and use them.
There are some phone users who like to tinker with system files to get the most out of their phones. They usually root their phones. Many instructions come with the warning not to root because this process can make your smartphone useless if you do it wrong.