The attacker attempts to upgrade an item (e.g. +6 → +7).
If the upgrade fails, they immediately crash the channel (WorldSvr process) where the attempt occurred.
Because the failure wasn’t committed to the database before the crash, a rollback restores the item in its pre-upgrade state, along with the materials.
This is repeated across multiple channels (CH1, CH2, CH3…), and only the successful upgrade is preserved.
The remaining channels are either crashed or left to rollback naturally, effectively erasing the failed attempts.