Context
One of the most frustrating buy-in failures is when you need the agreement of someone who is actually not negatively affected by the problem, perhaps barely associated with it, but they have a crucial role in the buy-in - even if that role is simply to get out of the way, and not block the implementation of a plan.
In that situation, a variation of the buy-in process is used to create the "what's in it for them" picture.
This method is also the base approach when persuading anyone in circumstances when you don't have the suite of buy-in tools with you. By focusing on the "WIIFT" your odds of success are automatically several notches higher than most conventional approaches.