慣れ and 油断: Familiarity and a lapse of caution
Compare familiarity that helps detailed work with letting one’s guard down. Preserve the possibility of accidents and the actor’s assessment of an opponent.
Familiarity that supports quick work
慣れ means familiarity or proficiency. 「細かい作業を素早くこなすには、ある程度の慣れが必要だ。」 says some familiarity is needed to carry out detailed work quickly.
「慣れから来る油断が事故につながることもある。」 says complacency arising from familiarity can lead to an accident. こともある presents a possibility, not an inevitable accident whenever someone becomes familiar with a task.
Letting one’s guard down
油断 means carelessness or complacency. 「慣れた作業でも油断してはいけない。」 warns against letting one’s guard down even during familiar work. Familiarity and a lapse of attention are different aspects of the activity.
「相手が弱いと思った油断が敗北を招いた。」 says complacency from thinking the opponent was weak led to defeat. The opponent’s weakness is the actor’s assessment, not an independently established fact about their ability.
Useful familiarity with continued caution
慣れ concerns familiarity that helps performance; 油断 concerns a lapse of caution. Needing familiarity for a task and needing to stay alert during that task can both be true.
The defeat example gives a cause in a particular case. It does not establish that all familiar tasks end in failure or that every proficient person becomes careless.
Do ある程度の慣れが必要だ and 慣れた作業でも油断してはいけない contradict each other?
Show the answer and why
No. The first concerns familiarity needed for the work; the second concerns maintaining caution even when the work is familiar. 慣れ and 油断 do not describe the same attitude.