頑張ると無理する
頑張るは努力を意味し、ポジティブな側面が強いですが、無理するはその努力が過剰になり、身体や心を害する可能性を含みます。
Trying your best and Overdoing: What’s the Difference? (Similar yet Different #082)
Trying your best means making an effort, and has a strong positive side, but overdoing it means the effort becomes excessive, and there is the possibility of harming your body or mind.