The toughest buy-in of all in conventional terms is when you're trying to gain agreement on the problem from someone who is at the root of the problem. Asking them to agree that their action (or lack of it) or decision ( or lack of it) is the cause of a problem isn't going to be well received. Using a Current Reality Tree to take them logically, step by step, through a process that mercilessly illustrates the terrific damage emerging from their action/decision isn't going to win you a friend.
So how do you go about it?
That's where the Evaporating Cloud shows one of its many strengths. Tyhe conflict diagram positions the person who might otherwise be on the defensive as being the VICTIM of a terrible, lose/lose conflict, rather than as the perpetrator of a problem. Moreover, it's ALWAYS true - it's not a trick. You make it clear that the SYSTEM is the problem, and that it's amazing that they've even been able to do a fraction of the great job they've actually done, in the circumstances. Then the CRT simply validates THIS stance, rather than attacking them.
For people who are very much involved in the subject matter and who will feel directly responsible for the identified Core Problem
For such a person, starting with the CRT and showing how the Core Problem for which they are responsible causes a myriad of problems is tantamount to setting them up for a lynching. They will either fight you tooth and nail (defensive) or leave the room and commit suicide :) (overcome with guilt).
Neither is the desired outcome!
1. Expose the cloud, re-worded if necessary to remove any signs or hints of finger-pointing. You want the cloud to position them 100% as the victim of a tug-of-war, of a dilemma that is not their fault. You use the cloud to give them ammunition to defend their position, and a way to clearly verbalize why it isn't their fault. Even the way you introduce the Cloud is important. For example,
"I don't see how you've been able to survive without stress leave, the more I looked closely at your position it seems to me you're absolutely trapped between a rock and a hard place."
"What do you mean?"
"Well, you're looking to be an effective Purchasing manager, right?"
"Well then, it seems to me that in order to be an effective Purchasing Manager you must keep production going, right? (Right). And to keep production going you have to keep lots of inventory on hand, especially given that the forecast is so dodgy and our clients have a habit of changing their mind at the last moment. But also, in order to be an effective Purchasing Manager you must Keep the CFO happy, which means keeping inventories down to a minimum, right? So it looks to me that you're in a lose/lose situation. Whatever you do comes back to bite you."
2. Now you can expose the CRT, because you've already taken a lot of time to show them it's not their fault as you build the Core Problem up to the UDEs. S/he is usually acutely aware of being at the heart of the conflict, even if they didn't think of themselves as responsible for the Core Problem. You don't have to be explicit about the benefits to them of eliminating or reducing the UDEs - they live with their consequences every day (Production on their back, Finance on their back).
3. Show the assumption(s) under the appropriate arrows in the Cloud that you are proposing to break, and the Injection(s) you have chosen.
4. Expose the Future Reality Tree, from the bottom-up. Let the person improve on it as much as possible. Trace every suggested potential negative side effect to it's conclusion, and deal with it together if necessary. The more of their ink on the page, the stronger their ownership.