foolish means one who is not sane, that is, that act recklessly, without having a good sense of their attitudes.
A fool is one who is insane, abnormal, a person who is difficult to deal with and understand. It is also often called unbalanced and irresponsible.
He practices his actions without fear or without believing that he is harming and mistreating others, since he is not properly aware of the evils he manages to devise and put into practice.
Etymologically, the word "foolish" originated from the Latin nonsense, which is formed by joining the element in-, which adds the sense of negation, and sense, which means “cautious” or “who has good sense”. Thus, the literal meaning of this word is "one who has no common sense".
For example:"Running at lunchtime in 40º degrees heat is nonsense" or "You were very unwise to leave the baby trapped in the car".
In 2011, TV channel Rede Globo presented the soap opera foolish heart, which addressed the relationship of several families.
The main focus of this novel was the conflict in the relationship between two brothers, protagonists of the story, and the tribulations arising from senseless love relationships.
See also the meaning of Insane.