It reminds me very much of this quote attributed to Gautam Buddha:
"Believe nothing merely because you have been told it. Do not believe what your teacher tells you merely out of respect for the teacher. But whatsoever, after due examination and analysis, you find to be kind, conducive to the good, the benefit, the welfare of all beings -- that doctrine believe and cling to, and take it as your guide."
(Since there didn't seem to be one for this month, and I just ran across a nice quote.)
A monthly thread for posting any interesting rationality-related quotes you've seen recently on the Internet, or had stored in your quotesfile for ages.