See, realize, etc. the error of your ways
Definition 1 of 1
Pro Tip 1/3Idiomatic Usage
The phrase is mostly used in discussions about moral or ethical behavior, often involving some kind of personal change or growth. 
After years of gambling, he finally saw the error of his ways and sought help.
Pro Tip 2/3Reflection Required
The phrase implies a moment of realization, suggesting that one has taken time to think about and understand their wrong actions. 
She realized the error of her ways after reflecting on the hurtful comments she had made.
Pro Tip 3/3Sincere Change
It is typically used to indicate a sincere intention to change, not just an understanding that something was wrong. 
He refused to admit the error of his ways at first, but his sincere apology showed he had changed.