One of my Rules for DMs is:

32. Support player ideas that are cool, creative, imaginative, and reasonable. That does not mean supporting ideas that are cool, creative, imaginative, and unreasonable.
a. The "Rule of Cool" must always be limited by the "Rule of Don’t Be Ridiculous".
c. If the idea is one you can see Aragorn, Conan, Captain America, or James Bond trying, allow it – for the right character. [Don’t let the Conan-clone play the James Bond stunt.]


I'm not sure that "limited" is the ideal verb for sub-rule a.
"Governed"?
"Constrained"?
"Bounded"?
Something else?