Why Do BSOD's happen?

Stop Errors :

Stop: 0x0000000A  IRQL_NOT_LESS_OR_EQUAL

STOP 0x0000001E KMODE_EXCEPTION_NOT_HANDLED

Stop 0x00000050 or PAGE_FAULT_IN_NONPAGED_AREA

Stop 0x00000024 or NTFS_FILE_SYSTEM

Stop 0x0000002E or DATA_BUS_ERROR

Stop 0x0000007A or KERNEL_DATA_INPAGE_ERROR

Stop 0x0000007B or INACCESSIBLE_BOOT_DEVICE

Stop 0x00000077 or KERNEL_STACK_INPAGE_ERROR

Stop 0x0000007F or UNEXPECTED_KERNEL_MODE_TRAP

Stop 0x000000C2 or BAD_POOL_CALLER

Stop 0x000000ED or UNMOUNTABLE_BOOT_VOLUME

Stop 0x0000021A or STATUS_SYSTEM_PROCESS_TERMINATED

Stop 0x00000221 or STATUS_IMAGE_CHECKSUM_MISMATCH

Stop 0x00000218 UNKNOWN_HARD_ERROR

Stop 0x000000F4 KERNEL_DATA_INPAGE_ERROR