How to Say "weak spot" in Spanish
The Spanish word for “weak spot” is “flanco” — C1 level.
English → SpanishC1
nounC1formal
a vulnerability in an argument or plan

Examples
Ese argumento es su flanco débil.
That argument is his weak spot.
No dejaron ningún flanco abierto en su estrategia de ventas.
They didn't leave any weak spots open in their sales strategy.
Atacó el flanco más vulnerable de la teoría.
He attacked the most vulnerable part of the theory.
Figurative Usage
In Spanish, as in English, military terms are often used to describe arguments or business competition.
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