Saber de qué pie cojea

/sa·ˈβeɾ ðe ke pje ko·ˈxe·a/

To know which foot someone limps on.

Frequency

ConversationVery common

JournalismCommon

LiteraryOccasional

AcademicRare

In English

to know someone's weak spot; **to know someone's weak spot**; **to know someone's Achilles' heel**; **to know what makes someone tick** (depending on the context); **to know someone's weakness**; **to know where someone's weakness lies**

Meaning

Saber de qué pie cojea means to know someone's weakness, understand what really motivates them or recognise their particular flaw or vulnerability.

Examples

Ya sé de qué pie cojea.

I know what his weak spot is.

Todos sabemos de qué pie cojea ese político.

We all know that politician's weakness.

Con el tiempo aprendí de qué pie cojeaba.

Eventually I learned what really made him tick.

Si sabes de qué pie cojea, es fácil convencerlo.

If you know his weakness, he's easy to persuade.

It often suggests knowing how someone is likely to behave.

Used when

they know someone's weak point
they understand another person's true intentions
they recognise someone's habitual flaw
they can predict how someone will react
they know where a person's interests or biases lie

Origin

The metaphor comes directly from physical limping.

A person who limps has one weaker leg.

Spanish transfers this image to character, suggesting that everyone has a particular weakness or vulnerability.

Knowing de qué pie cojea means knowing exactly where that weakness is.

Cultural note

The expression does not always imply a moral defect.

The "weakness" may be:

excessive ambition,
vanity,
generosity,
love of money,
pride,
or any predictable tendency.

The important idea is understanding someone's characteristic point of vulnerability.

Did you know?

Spanish often uses parts of the body to describe personality:

Saber de qué pie cojea → to know someone's weakness.
Tener buen corazón → to have a good heart.
No tener pelos en la lengua → to speak one's mind.
Meter la pata → to put one's foot in it.

Body-based metaphors are among the richest sources of Spanish idiomatic expressions.

For English speakers

Do not translate the expression literally.

English speakers would never say:

I know which foot he limps on.

Instead, use expressions such as:

I know his weak spot.
I know his Achilles' heel.
I know what makes him tick. (when referring to motivation)
I know his weakness.

Choose the translation according to whether the emphasis is on weakness or personality.