If the drive belt repeatedly falls off the drive belt pulleys, this is because of pulley misalignment.
An extra load that is quickly applied on released by an accessory drive component may cause the drive belt to fall off the pulleys. Verify the accessory drive components operate properly.
If the drive belt is the incorrect length, the drive belt tensioner may not keep the proper tension on the drive belt.
Excessive wear on a drive belt is usually caused by an incorrect installation or the wrong drive belt for the application.
Minor misalignment of the drive belt pulleys will not cause excessive wear, but will probably cause the drive belt to make a noise or to fall off.
Excessive misalignment of the drive belt pulleys will cause excessive wear but may also make the drive belt fall off.