One key is vested interest - the extent the attitude is relevant, which is whether the object/issue might have important consequences for the person holding the attitude.
Greater interest, stronger impact
People's behavior usually supports the attitude
Attitudes formed on the basis of direct experience can exert stronger effects on behavior than ones formed indirectly.
Communicators who seem more credible & members of groups we identify with have more influence on attitudes. Attractive communicators, people who speak rapidly, & people who exhibit greater confidence are most persuasive