When combined, the literal meaning is “strange thoughts opening the heavens.” This powerful imagery suggests an idea so unconventional and out-of-this-world that it breaks through the normal confines of reality (represented by the sky). It's not just a bad idea; it's an idea that defies logic and common sense on a cosmic scale.
The usage of 异想天开 reflects a strong cultural emphasis on pragmatism (脚踏实地, jiǎo tà shí dì - “feet on solid ground”). While Western business culture might celebrate “blue-sky thinking” or “thinking outside the box” as the seeds of innovation, 异想天开 is rarely seen in such a positive light in a Chinese context. A useful comparison is the difference between being a “visionary” and being “fanciful.”
Therefore, this idiom serves as a social corrective, a way to gently (or not so gently) remind someone to be more practical and realistic. It underscores a cultural preference for steady, grounded progress over wild, unpredictable leaps of faith.
异想天开 is a common idiom used in various settings, from business meetings to family discussions. Its connotation is almost always negative and dismissive.