I know "jump off the deep end" means to abruptly step into something but I'd like to know what it means in terms of actual physical jumping - because you usually "jump off" something not deep. What does a native speaker imagine when hearing the phrase?

  • 1
    Think about swimming pools.
    – Davo
    Jul 28, 2017 at 16:32

1 Answer 1


The relates to jumping (or diving) into the deep end of a swimming pool.

In the deep end of the pool, the water is too deep for you to stand on the bottom, so you are forced to swim. It's a metaphor for coping with the unfamiliar, especially when you are not properly prepared. "Deep water" is a metaphor for the unknown, so when you jump into deep water you don't know what might happen, or what might be lurking under the surface.

A related idiom is sink or swim. When you jump off the deep end, you have choice but to learn to swim, otherwise you're going to drown.

In addition, go (or jump) off the deep end has become synonymous with go crazy, or lose one's head:

lose one's head (v), "To behave irrationally or to lose self-control, especially in a distressing situation"

The connection here to swimming pools is less clear, although it's probably connected with the idea of deep water being (literally) unfathomable, meaning that you have no idea what someone who has "gone off the deep end" is going to do.

  • 1
    Similarly, in a situation that goes beyond your intent or control, you can be "in deep water" or "in over your head".
    – user3169
    Jul 28, 2017 at 19:54
  • I just still don't understand the preposition "off". Doesn't "jump off" mean "jump from". "Jumping from the deep end" sounds like the opposite of what it should mean ("jumping to the deep waters/end").
    – Probably
    Jul 29, 2017 at 4:23
  • @Probably I agree that it doesn't make sense. How can you jump off from the deep end of a pool? I expect that, originally, it was, "Jump off the diving board. into the deep end of the pool" and the idiom got shortened over time.
    – Andrew
    Jul 29, 2017 at 13:03
  • I have always heard it as, "jump in at the deep end" Mar 3, 2021 at 11:00

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