How is “to be sure” used?

In Tenet (2020), one line is: “That's the only way to be sure.”

Which movie is “to be sure” from?

The clip at the top of this page is from Tenet (2020).

to be certain, or to make sure, often as a check or precaution; used to admit that sth is true

formal · Se oye en 25 películas

Definición editorial90% de las películas
to be certain, or to make sure, often as a check or precaution
Oxford10% de las películas
used to admit that sth is true

Definiciones del Oxford Advanced Learner's Dictionary, 9.ª edición

That's the only way to be sure.

En 8 películas · n.º 1