How is “sink or swim” used?

In Christopher Robin (2018), one line is: “It's sink or swim.”

Which movie is “sink or swim” from?

The clip at the top of this page is from Christopher Robin (2018).

It's sink or swim.

5 作品で登場 · 1 本目

イディオム

to be in a situation where you will either succeed by your own efforts or fail completely

5 本の映画に登場

to be in a situation where you will either succeed by your own efforts or fail completely
The new students were just left to sink or swim.

定義：Oxford Advanced Learner's Dictionary 第 9 版