Possible Clues:

• “S” term meaning “to take a dip”?
• If you don't succeed, you'll fail -- as you may in the pools?
• Success-versus-failure metaphor, and what can be found at the starts of the answers to the starred clues
• Challenge for somebody thrown in the deep end, in two senses
• Succeed-vs.-fail choice
• Stark alternatives, after making a splash?
• Cope (or not) unaided