Attitudes stemming from are more confidently held, more enduring, and more resistant to competitors' messages than attitudes originating from promotional messages only.

Attitudes stemming from PRODUCT USAGE are more confidently held, more enduring, and more resistant to competitors' messages than attitudes originating from promotional messages only.
Product usage enables a customer to observe the pros and cons of a product. This increase the level of confidence n the attitude of the customer, towards that product.