It is no use crying over spilled milk when we fail in exams.
To regret
Crying over spilled milk is a proverb that means to be upset and to regret something which has already happened and there is no chance to change the situation.
E.g: Sita never put effort but has the habit of crying over spilled milk.
One must work hard so that they do not have to cry over spilled milk at the end.