Tagging onto what dt posted:

Clemenza stayed with Michael out of loyalty, not some penetrating insight about Michael's hidden strength. Tessio assessed the situation as he saw it, and came to the logical conclusion based on what he saw. That's why he was "smarter."

The key word is "always," as in "Tessio was always smarter." That means that Tessio was smarter than Clemenza in other situations that we don't know about from the film.


Ntra la porta tua lu sangu � sparsu,
E nun me mporta si ce muoru accisu...
E s'iddu muoru e vaju mparadisu
Si nun ce truovo a ttia, mancu ce trasu.