the meaning of slippery circularity

[guzhao67]

Dear teacher: could you explain the meaning of "slippery circularity" in the following sentence for me please? And what's the meaning of the whole sentence exactly? (i'm not sure ...)
... and the customary explanations often retain a certain slippery circularity which defeats any attempt at systematic comparison and evalulation.
thank you very much

[susiedqq]

You may hear the expression "talking in circles," which means the conversation goes around and around in terms of subject matter. It is difficult to understand.

It sounds like customers are having a difficult time explaining their needs, wants or problems.

"Slippery" may mean that the conversation can 'slide or veer off" into another subject area and the real issue becomes lost in all the talk.

[tedtmc]

customary explanations often retain a certain slippery circularity

explanation which beats about the bush, in a rambling/meandering manner

not a teacher