'Foolish' in the Bible

Samuel said to Saul, “You have been foolish. You have not kept the command which the Lord your God gave you. It was at this time that the Lord would have permanently established your reign over Israel,

My lord should not pay attention to this wicked man Nabal. He simply lives up to his name! His name means 'fool,' and he is indeed foolish! But I, your servant, did not see the servants my lord sent.

Then Saul said, I have done wrong: come back to me, David my son: I will do you no more wrong, because my life was dear to you today truly, I have been foolish and my error is very great.