Some time ago I have a read a very famous book of Allen I. Holub "Enough rope to shoot yourself in the foot" (this book on openlibrary.org). I have read it in Russian and the book was titled with exact, i.e. word-by-word translation of the original English title. And, as you can imagine, it was totally nonsensical. Then I became interested in the meaning of the original title.
I found out that this is a nice play of two idioms:
give somebody enough rope (to hang themselves) meaning to allow someone to do what they want to, knowing that they will probably fail or get into trouble
to shoot yourself in the foot meaning you do something that damages your ambition, career, etc.
I started to think about better translation, but the question is: can you think of a short phrase in English without idioms to keep the same meaning? It would be also interesting if there are proverbs or set expressions with the same idea.
Best Answer
Holub employs a mixed metaphor (as Robusto suggested) and the descriptions of the book allude to at least one other expression, which is "just enough to be dangerous" (as in "I/You/They know just enough to be dangerous.").
As with most metaphors, they are designed to evoke a mental image of equivalence. In this case, Holub appears to be addressing some particular aspects of computer programming where he believes that programmers are knowledgeable enough (enough rope) to be dangerous (shoot foot) and therefore they are "a danger" to the programming world.
Using a mixed metaphor is often done for humorous effect, which appears to be Holub's intent here. As this review states "Holub manages to make a serious subject refreshingly readable by sprinkling the text with humor and insight."
If a mixed metaphor like this were to have a commonly used substitute, the substitue would probably lose the full effect of the metaphor. But you might say simply use "Programmers know just enough to be dangerous" (which isn't idiomatic, but requires context), which I already mentioned. Stated alone, it doesn't evoke the same image as a hanging and an unintended discharge of a weapon.