These rules apply whether you are an external partner or an internal one.
Rule number 1. Resistance is never universal. There are always pockets of power or pockets of discomfort. How you move them forward is simply an art. There is no such a thing as an entire organization resistant to change. Thinking that way is a trap. See rule number 10 (but not yet, keep reading)
Rule number 2. The system will always protect itself against solving the problems that it creates. Don’t expect sudden conversions. Turkeys don’t like Christmas. Start where there may be less antibodies. Usually in the edges of the organization, not the core-core
Rule number 3. Don’t overwhelm people with incredibly well-crafted and complex plans. Spend the energy helping them to visualize an attractive outcome that ‘can’t be refused’.
Rule number 4. People who ask for examples of where else something has been done before successfully, don’t really mean that. They mean ‘I need comfort’. If there is a deep discomfort, no number of examples will move them. Comfort can be given in many ways, not just case studies.
Rule number 5. Talk about the cost of not doing something much more than the cost of doing it.
Rule number 6. Your fans may not be your buyers (whether a consultant or an internal partner). Your readers may not be your clients. Your faithful and grateful audience may have no power (both internally in an organization or as external partner)
Rule number 7. This is for external consultants and partners. Be prepared to say ‘you are not a good fit for us, we can’t help you. (Possibly with an added, ‘but we can give you the phone number of our competitors’)
Rule number 8. Whether external or internal partners, never, ever, ever present a full plan to the entire Leadership Team or Board without having gained previously individual buy-in at least in 2/3 of the members.
Rule number 9. If you get a super-excited and super-enthusiastic group of people who say ‘this is so good that it should be done across the board, not just us, let’s involve other higher or broader levels’, this is really bad news. Chances are it will never be done.
Rule number 10. ‘Readiness’ is a red herring. Nobody is ever ready. Don’t aim at full rational and emotional convincing of all. That the powers let you start, even if not fully convinced, is 100 times better than waiting for total enlightenment. People become ‘ready’ ( and that includes leadership teams) when they see good things already happening. Readiness is most a post-hoc state of mind.
Bonus rule: Consider this line by Robert A Heinlein (1973): ‘A fool cannot be protected from his folly. If you attempt to do so, you will not only arouse his animosity but also you will be attempting to deprive him of whatever benefit he is capable of deriving from experience. Never attempt to teach a pig to sing; it wastes your time and annoys the pig’. Sometimes singing is just impossible, get over it.