Weapons have a very small chance per hit of breaking, to make it a memorable event when it happens.

• Blessed, positive enchantment, or an artifact: never breaks.
• Uncursed and +0: 1/32000 or 1/32768 chance of breaking.
• Cursed or negative enchantment: 1/1000 chance of breaking.
• Chance is multiplied by 20 if the weapon is thrown and did not hit a monster.