To justify a decision, action, or idea means to show or prove that it is reasonable or necessary 证明…有理，正当 为…辩护
The end justifies the means.
The new features of iphone Xs cannot justify its hefty price tag.
他的决定从经济上完全可以理解，但从道德上很难成立。His decision can be justified from an economic point of view ，but can hardly be ethically justified.
他想为自己的缺席辩解 但是理由不行 He tried to justify his absence with lame excuses.
