force of habit 习惯了；出于习惯；习惯使然

【例句】
By force of habit I always put keys in my coat pocket.
我习惯把钥匙放在上衣口袋里。

Oh, sorry. I guess I tried to light one by force of habit.
噢，抱歉。我想我是习惯性地点烟抽。