When someone talks about taking a look in the mirror, they mean they are going to take some time to look at themselves honestly and objectively. The idea is to be 100% honest with ourselves so that we can identify and then fix our weak points.
Also, it is sometimes easy to criticize others, but we often overlook those same faults in ourselves.
Here are a few examples:
“After his poor performance on the mid-term test, Nigel had to take a look in the mirror. He realized that he needed to spend more time studying and less time partying.”
“The manager blamed his staff for the team’s poor performance. But I think he should take a look in the mirror first!”
誰かがtaking a look in the mirrorについて話していたら、それは時間をかけて正当に、客観的に自分自身を見るという意味です。100%自分に正直になることで自分の弱点を見極め、そして直すことができるのです。