you take the plunge, you decide to do something or commit yourself even though you know there is an element of risk involved

Just jump in the deep end and learn to swim later.

"take the plunge”是一种习惯用法，it means "take a bold decisive step, especially after thinking about it for some time." 通常是指经过一番考虑后果断采取的某种冒险行为。可以直接理解为：“做一次冒险尝试。”

“take the plunge” = take a risk or take a chance