What is the meaning of this quote Psychology which explains everything explains nothing and you are still in doubt?

where did you find the quote it be easier to answer in a context..
I find that overall if something explain everything usually explains nothing because it itself is not explained.
Doubt is something we cannot simply avoid. Certainty is possessing all knowledge or being error proof. We can feel certain however we cant attain certainty.

"Doubt is not a pleasant condition, but certainty is absurd."
- Voltaire (François Marie Arouet), 1694-1778


I heard a similar version of this qoute in Polish
If something is for everything its for nothing
but It was referring to medicine and other things which claim to do everything but it simply fails at everything and had completely different meaning.