I recently saw an image where this quote
Non temete nuotare contro il torrente, è d'un anima sordida pensare come il volgo, perché il volgo è in maggioranza
is attributed to 16th Century Italian philosopher Giordano Bruno.
Searching for it on Google returns several results (mostly people using it as "signature" in discussion forums, this article, and the quote at the beginning of this book) attributing it to Giordano Bruno, but I can't find it anywhere on Wikiquote (for example).
The sentence can be translated to:
Do not be afraid to swim against the torrent [i.e. upstream], it is of a sordid soul to think like the common people, because the common people are always the majority.
Did Giordano Bruno ever said anything to that effect?