Negligence or carelessness; lack of attention or preparedness that can lead to mistakes or accidents.
油断していたら鍵をなくしてしまった。
Because I was careless, I lost my keys.
油断大敵という言葉の通り、最後まで気を抜いてはいけない。
As the saying 'carelessness is a great enemy' goes, you must not let your guard down until the end.
油断してミスを招くことが多いので、注意深く仕事を進めよう。
Carelessness often causes mistakes, so let's proceed with work carefully.