All Western legal/constitutional systems nowadays have a basic right against self-incrimination (e.g. the Fifth Amendment in the US).
Under this right, what would keep me, as a witness in a criminal case, from refusing to testify with the following argument?
I will not answer your question because the answer would incriminate me of a criminal offence. I will not specify the offence or the way the answer would incriminate me because doing so would incriminate me, in a way that will not specify because doing so would incriminate me, in a way that will not specify … (ad infinitum)