Sales managers either love a new item so much they think it will outsell everyone, or they think it is a dud and under forecast equally badly.

Sales managers either love a new item so much they think it will outsell everyone, or they think it is a dud and under forecast equally badly. The technical people, become so enamored with their inventions that they lose all objectivity too. What I like is forecasting done by independent people--project managers or new products managers in separate departments. Mention good ways of keeping sales managers and technical researchers out of forecasting? Should they should be excluded?"