When describing an idiot, "一根弦的傻子"? 一根弦的傻子


From what I see, "An idiot with one root/string?"

I don't really understand where the meaning would be taken from. Would an English equivalent be something like "An idiot with only one brain cell"?
As Pedroski has explained, 一根弦的傻子 or 脑子一根弦 refers to those who clings to one idea. 一根弦 can be interpreted as &quot;single-minded&quot;. But note that it is not necessarily a derogatory term.
For example, in the following sentence,

一根弦的傻子，也能熬出头。
A single-minded fool can eventually survive from the nights and succeed as well.

一根弦 implies that the &quot;fool&quot; is determined and strong-willed and will not give up on what he/she has been pursuing for.