さっぱり Sappari やっぱり Yappari

さっぱり Sappari is one of those Japanese words that I can't find any good explanation for. So, here's my descriptive reasoning for it:

First learn やっぱり yappari. "Ya" has the same English meaning as yes/ya/yup. So, it roughly means "Yup, I've finally realized it". The key point to note is the sentiment or agency (timeliness) of this statement, which conveys that a process has been undergone before reaching the result.

For さっぱり Sappari, the "Sap" denotes being washed, or "soaped" in English. In a negative context, it's "sapped". The "-pari" part carries the same sentiment as in "yappari".

Therefore, さっぱりわからない Sappari wakaranai means "I have been sapped of logic the more I tried to understand it till the point that I'm now completely fuddled". So, rather than a "I have no idea how to understand this", it's more like "I ran out of ideas to understand this".

And 売上がさっぱりだ Uriage ga sappari da means "the sales numbers have been wiped clean from the sales chart".