Nip the evil in the bud

This everyday expression means that unless an individual is made to mend his ways in the early days, it will be too late to change him later.
The expression comes from one of Aesop's Fables, ‘The Thief and his Mother’. Aesop lived between c. 620-560 BCE.

A woman had an only son, whom she loved very much. One day he stole an object from another schoolboy and brought it home to show his mother.
Instead of scolding him, she showed no disapproval and ignored it.
From then on, the schoolboy stole something everyday and brought it home, but his mother never said a word of disapproval.
As the schoolboy grew into a man, he continued stealing bigger and bigger things. Finally, he ended up committing a murder. He was tried and sentenced by a judge to hang.
When his mother arrived at the prison to see him, he bit her ear. The judge asked him why he had done that, the man replied that if she had stopped him stealing in the early days, he wouldn’t be waiting to be hanged now.
The moral is nip the evil in the bud.