1. go into a challenging new situation without help or preparation
jump/dive in at the deep end and take on a risky challenge
If you 'jump in' or 'dive in at the deep end', you do something new or challenging with little or no preparation or experience. When you 'dive in at the deep end', you find yourself immersed or involved in something without being adequately equipped to handle the situation. People often use this phrase to talk about their first day at work or in a new job being 'thrown in at the deep end', without much instruction or guidance.