Introspection is easy to misunderstand. Superficially, the introspectionist seems to say: “Here’s how my mind works; I infer that some other minds (or many others, or all others) work the same way.” But that is not the introspectionist proposition. The introspectionist is a dance teacher, not a dancer. He demonstrates a move and then says, you try it! His goal is not to explain dancing by showing you how he does it. His goal is to explain dancing by showing you how to do it. Then you will reach your own conclusions.
Thus the introspectionist goes in one leap from the weakest possible argument to the strongest — from a weak argument based on his experience alone to an irrefutable one based on yours.