One thing I find helpful, is to outsource this to my mental model of other people, or actual other people. If you come at them with “This is definitely true”, what kind of objections do they come up with? Not just explicit objections that they say, but also implicit objections that they don’t know how to articulate. Once you’ve explored that space and know that all roads lead to them being fully on board—again, not just in explicit claims but in revealed belief as well—then you know that at least they can’t come up with a reason you might be wrong.
It’s still only as good as your other people, but if no one you know can find fault in your reasoning that’s not a bad start.
One thing I find helpful, is to outsource this to my mental model of other people, or actual other people. If you come at them with “This is definitely true”, what kind of objections do they come up with? Not just explicit objections that they say, but also implicit objections that they don’t know how to articulate. Once you’ve explored that space and know that all roads lead to them being fully on board—again, not just in explicit claims but in revealed belief as well—then you know that at least they can’t come up with a reason you might be wrong.
It’s still only as good as your other people, but if no one you know can find fault in your reasoning that’s not a bad start.