What is the best action to take if the manager says something isn't right and you know the right thing?

its  differ according to the weight of this answer 

1- if it will affect in strategic decision or affect the business in short term or even long term  , we must clarify for him without challenging through team brain storming , discussion to put his mind and hand in the right thing 

2- if will not affect the business so i can clarify it through time