千慮 せんりょ いち しつじゃなかったです
senryono ichishitsujanakattadesu

Noun
Desu Copula

The polite, past negative form of 千慮の一失

1. Wasn't a single mistake after a thousand considerations.; Wasn't careless despite thorough thought.

Past/Perfective
Negative
Polite
Casual Register