"Sink or swim" is a situation where you will either fail or you will find a way to succeed. " Example: "Sales is not an easy job here. We give you two weeks training, then it's sink or swim." If you are thrown into the water, you will either sink to the bottom or you will swim to safety. You will either fail, or you will find a way to succeed, in a situation that is sink or swim. Example: "How do you interview new teachers here?" Reply: "We just put them in with the kids, and see how they do. It's sink or swim." Sink or swim" means that you will either succeed, or you will fail completely, at what you are trying to do.