短所を改善する

You will mostly use this as a verb phrase. It often appears in the form 短所を改善したい (I want to improve my weaknesses) or 短所を改善しようと努力しています (I am making an effort to improve my weaknesses). It is a bit formal because of the word 改善. This word is often used in business for 'process improvement.' So, when you apply it to yourself, it sounds like you have a serious plan for growth. You can use it when talking about habits, social skills, or work performance.

The absolute best time to use this is during a job interview in Japan. Interviewers almost always ask about your 短所. Answering with how you are 改善する-ing them shows you are a 'kaizen' person. It is also great for performance reviews with your boss. You might also use it in a heartfelt conversation with a partner. For example, if you are always late, you might promise to 短所を改善する. It shows you take their feelings seriously. It is also perfect for New Year's resolutions or self-help journals.

Avoid using this for physical objects. If your phone screen is cracked, you don't 改善 it; you 修理 (repair) it. Also, be careful using it for other people. Telling a friend, "You need to improve your weaknesses," sounds very cold and robotic. It is like you are treating them like a factory machine. In casual settings with friends, this phrase can feel a bit 'stiff.' If you are just talking about a bad habit like biting your nails, use a simpler word like 直す (naosu).

This phrase is the cousin of the world-famous 'Kaizen' philosophy. In Japanese culture, there is a deep respect for 'sunao' (being honest and coachable). Admitting your 短所 is not seen as a sign of weakness. Instead, it is seen as a sign of strength and self-awareness. There is a cultural expectation that everyone is a 'work in progress.' This is why self-reflection, or 反省 (hansei), is taught from kindergarten. Improving yourself is considered a lifelong duty to society and yourself.

If you want to sound more casual, use 短所を直す (tansho o naosu). This is the 'bread and butter' version for daily life. If you have a weakness that feels like a huge mountain to climb, use 短所を克服する (tansho o kokufuku suru). This means 'to overcome' or 'to conquer' your weakness. If you want to focus on things you are just bad at (like math or cooking), you can say 苦手を克服する (nigate o kokufuku suru).