Does 外行的想法 mean "rookie mistake"? I found this sentence and its translation on tatoeba.org. Is there a better way to translate it into English?

這是外行的想法。
That's a layman's idea.

I looked up 外行, and it does mean amateur or layman, but I've never heard anybody use the phrase &quot;layman's idea&quot; in English. Perhaps a better translation would be as simple as, &quot;That's a dumb idea.&quot; Or does the Chinese phrase emphasize that it's a bad idea because the person is inexperienced? If so, perhaps it would be best to translate as, &quot;That's a rookie mistake.&quot;
English is not my mother tongue, but I would translate 外行的想法 as "unprofessional opinion" or "amateurish opinion".
外行 is the opposite of 内行, which means expert, adept, experienced, an expert, a professional, so the emphasis is as you mentioned on the fact that the person is not experienced.