胸先 むなさき さん すんじゃありませんでした
munasaki sansunjārimasendeshita

Noun
Desu Copula

The polite, past negative form of 胸先三寸

1. It wasn't within my capabilities.; It wasn't what I'm capable of.; I wasn't up to it.

Past/Perfective
Negative
Polite
Terminal Form