心安理得

  1. to have a clear conscience
  2. to have no qualms about sth

“feel at ease and justified; one's conscience is void of offence”

得:适合。自以为做的事情合乎道理,心里很坦然。

示例 到后来忘却了真,相信了谎,也就~,天趣盎然了起来。(鲁迅《病后杂谈》)