fool to oneself

Noun

One who knowingly makes a decision or takes action that is to his/her own disadvantage.

Japanese Meaning

自分自身をだます者、自分に不利益な判断や行動を自覚してとる人

リスクを承知でありながら、彼は怪しい計画に全財産を投じて、自分の利益に反する行動を選ぶ人のように振る舞った。

Sense（1）

One who knowingly makes a decision or takes action that is to his/her own disadvantage.

By swimming, drunk, late at night and alone, he was being a fool to himself.

fools to themselves

（ plural ）