To be great is to be misunderstood.
Emerson suggests that people who think or act independently may be misunderstood because their ideas do not fit established expectations. In Self-Reliance, he places the remark among examples of influential figures whose views were criticised or rejected in their own time. Misunderstanding is therefore presented as a possible consequence of originality and nonconformity.
The statement does not mean that being misunderstood automatically makes someone great. Rather, Emerson argues that fear of misunderstanding should not prevent a person from expressing a considered conviction. New or unconventional ideas may initially appear inconsistent, strange or mistaken to others, particularly when they challenge familiar assumptions. The quotation reflects his broader defence of self-reliance: individuals should judge their ideas by their substance rather than by immediate public approval. Independence may carry social costs, but Emerson regards willingness to bear those costs as an important part of intellectual and personal integrity.