Anger is an acid that can do more harm to the vessel in which it is stored than to anything on which it is poured.
I'm not sure what "anything on which it is poured" actually means. I looked up the dictionary searching for "pour" and "pour on" and tried to construct the sentence but I got more confused. If you poured the acid on "anything", isn't it the same thing as storing the acid in since the "acid" would still remain? Or is it just the matter of degree?