This phrase literally translates to 'where it hurts the most'. It is used to refer to hitting someone (mostly metaphorically) in their most vulnerable or sensitive spot or using someone's weakness against them.
Examples
- Spanish: Ella sabía que para ganar la discusión debía atacarlo por donde más le duele: su orgullo.
- English: She knew that to win the argument she had to hit him where it hurts the most: his pride.