1. a situation in which someone/something must succeed without any outside help or fail
in such a competitive environment, it is a case of sink or swim
he idiom 'sink or swim', means to succeed or fail on your own using your own skills and strengths without outside help. You will often hear the phrase 'It's time to sink or swim' meaning that something will either fail or be successful. This is an expression that can be used in both social and professional contexts.