What two factors inhibit the ability of rivals to imitate a firm's most valuable resources and capabilities?

I think the most applicable answers are,

*The possession of expertise, knowledge and skills that the competitors do not possess

*Having the access to unique resources and legal protections (such as patent rights)

Explanation:

When you have the intellectual and skill. capacity to harness the maximum out of a Resource and that it is a unique one, then the competition have one way to imitate you.

Moreover, once you have the legal protection and/or the exclusive access to a certain resource or to a technology, then the competitors can't imitate you as well.