理直气壮 (lǐ zhí qì zhuàng): Be bold and straight (adjective/idiom) — Meaning & Stroke Order

Faced with unreasonable accusations, she defended her position boldly and with justification.

On what grounds can you so boldly demand that others cooperate with your plan?

She refuted the other's point with sound reasoning, appearing confident and justified.

At the friend gathering, he explained the special reason for his lateness with a confident and justified tone.