John Watson is so hidden. We never see his bedroom. We never see his sister. We never see any of his associates or acquaintances from before he met Sherlock. He smiles when he is angry and limps when he is sad and beyond that we know nothing.
He wept openly at Sherlock’s grave and we only see that reflected in the gravestone (through a glass darkly). We get his real face again only after he’s wiped away his tears and drawn himself up to attention.
We get to see him directly only when he’s put his mask back on.
(But his feet were bare in Baker Street. Alas, too late…)