A powerful idea communicates some of its power to the an who contradicts it. Partaking of the universal community of minds, it infiltrates, grafts itself on to, the mind of him whom it refutes, among other contiguous ideas, with the aid of which, counter-attacking, he complements and corrects it; so that the final verdict is always to some extent the work of both parties to a discussion. It is to ideas which are not, strictly speaking, ideas at all, to ideas which, based on nothing, can find no foothold, no fraternal echo in the mind of the adversary, that the latter, grappling as it were with thin air, can find no word to say in answer.
(Marcel Proust, Within a Budding Grove, In Search of Lost Time; trans. Moncrieff, Kilmartin, and Enright)
This reminds me of a saying by Oscar Wilde: "When people agree with me, I always think I am in the wrong." Similarly, Proust suggests that when your ideas encounter no opposition, they are simply flimsy, lacking robustness; they lack power. Only powerful ideas are complex enough, rich enough, to invite opposition. Proust's phrasing, however, is not just that of opposition, but of cooperation in opposition. Strong opposition suggests a "fraternal echo," a camaraderie that cannot occur when lesser ideas are proposed. Two or more figures--sharing in the "universal community of minds"--oppose one another and contribute to one another; they pull apart among plural minds and come together in the universal community with a composite resultant that bears the marks of one another's thought. It is almost the stereotyped Hegelian thesis-antithesis-synthesis, but the antithesis can only have authority if the thesis was powerful; the synthesis is almost the child of two minds coming together in cooperation and opposition, being born with distinctive traits from both of its parents.