Complex sentence: When there is no attitude or behavior change it can be concluded that a negative violation has occurred (possibly a boomerang effect) and when an attitude or behavior change does occur some have concluded a positive violation of expectations must have occurred.
Split into simpler sentences: When there is no attitude or behavior change it may be concluded that a negative violation has occurred (possibly related to a boomerang effect). Conversley, when an attitude or behavior change does occur it may be easy to conclud a positive violation of expectations must have occurred.