Theory Formation and Paradigm Shift

A friend recently asked me about the elements of what a theory is and how it can be more certain. I've been thinking about it, and I think one of the things is that one of the ways it could be more certain is to be less susceptible to paradigm shifts - AKA, that it won't change everything if we change just a couple things around. Or is a paradigm shift more than that? Can we measure what is susceptible to such a shift? It could certainly be helpful if we could...