Scaling in - Good when you have a realistic target (not an imaginary one you made up yourself), and how far you are into the trend, if you are 10% into the trend, keep scaling, no big reversals, 80% into the trend, don't be scaling, big reversals going to kick your ass in the face.
Scale out - Get out when price becomes not predictable, as it means, if you don't know where its going, its time to get out on most of the position, if you do know where price is going, stay in
Realize on both whats removed: hope.