In an idea development process, there is always a danger of getting excited about some important elements (functions, design, et cetera) and losing sight of shortcomings or immaturities.
With the method motorboat this view is sharpened. Here, the focus is on the components that need improvement or perhaps prevent success.
The image of a motorboat with an anchor out is very evocative for the participants and helps them identify the braking, hindering aspects.