Step by step, one slips towards the bottom:

1. One should be blunt with those who are wrong.
2. One is blunt when one is right.
3. When one thinks to be right, one is blunt.
4. One is wrong and blunt.

http://charles.plessy.org/Debian/debiâneries/pente-glissante/

(Какие тут поставить теги? Ничего не приходит в голову.)