Whenever I face this, in my own analysis or others, I apply the "let's find out" tactic. Instead of doing nothing I'll propose that we do X which I surmise as a

Whenever I face this, in my own analysis or others, I apply the "let's find out" tactic. Instead of doing nothing I'll propose that we do X which I surmise as an option that a) is non-destructive and reversible, b) has a chance of working out. [You can add your own criteria, e.g. fast/easy, simple, etc] At the very least we'll learn something. When someone else is stalling, I'll phrase it something like "Unless someone has specific reasons against investigating X, I propose we prototype it and see where it goes." If still unsure, prototype Y. After that you usually realize there's not much point prototyping yet another an simply choose one and see how far it can go.