Vito's refusal "was not the act of a friend," as Barzini noted at the summit meeting. As the head of one of the virtual coalition of five families, he "must share" his resources. Without that assistamce (judges, political protection, etc.) the others could not do the business they wanted to do. When Barzini pointed this out, he hit it on the nail - Vito's refusal was seen as betraying an unspoken but well understood tenet of the uneasy coalition, and perceived as endangering the bisseniss. Those remarks allowed Vito to realize immediately that it was "Barzini all along" - not that pimp Tattaglia.