'Foolish' in the Bible

And Samuel said to Saul, You have done a foolish thing: you have not kept the rules which the Lord your God gave you; it was the purpose of the Lord to make your authority over Israel safe for ever.

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.