stole イディオム
lock the barn door after the horse is stolen
be careful or try to make something safe when it is too late If you try and prevent a flood after the rains have started it is like locking the barn door after the horse is stolen.
Stolen fruit is the sweetest.
What is forbidden is the most tempting.
lock the barn door after the horse is stolen|after
To be careful or try to make something safe when it is too late.

A proverb.
After Mary failed the examination, she said she would study hard after that. She wanted to lock the barn door after the horse was stolen.