Every castle is undefeated… for some while!

難攻不落
nan.kou.fu.raku

Literally: difficult – attack – not – fall

Alternately: Nigh impervious to assault. Difficult even to attack, much less to actually bring down, like a near-impregnable castle. By extension, a situation where things don’t go as planned, expected, or desired.

Notes: Sources suggest that this compound was formed in the Sengoku period, and note wryly that few of the era’s supposedly-invincible castles remained undefeated.

Kumamoto Castle, which bills itself as Japan’s most 難攻不落 fortification.