What does “make certain” mean?

to make sure that something happens or is the case

How is “make certain” used?

In Casablanca (1943), one line is: “...and she did a bad thing to make certain of it...”

The clip at the top of this page is from Casablanca (1943).

...and she did a bad thing to make certain of it...

3 作品で登場 · 1 本目