jump in/be thrown in at the deep end
jump in (at) the deep end
To begin doing something very complex and/or unfamiliar, especially suddenly and without guidance, assistance, or preparation. A: "But I've never worked in sales before!" B: "You'll be fine, just jump in the deep end and try your best!" I'm a little nervous about starting my graduate degree program, but I'm determined to jump in at the deep end and give it a go. Those who go the furthest in life are the ones willing to jump in at the deep end when a great opportunity arises.
jump (or be thrown) in at the deep endface a difficult problem or undertaking with little experience of it. informal
jump in/be thrown in at the ˈdeep end(informal) try to do something difficult without help when you are not prepared or know very little about it: On the first day of her new teaching job, she was thrown in at the deep end and was told to teach the most badly-behaved class. ♢ I didn’t know anything about business when I started. I just had to jump in at the deep end.
This phrase refers to the deep end of a swimming pool, where it is too deep to stand.