The Human Chord by Algernon Blackwood

As a boy he constructed so vividly in imagination that he came to believe in the living reality of his creations: for everybody and everything he found names—real names. Inside him somewhere stretched immense playgrounds, compared to which the hay-fields and lawns of his father’s estate seemed trivial: plains without horizon, seas deep enough to float the planets like corks, and “such tremendous forests” with “trees like tall pointed hilltops.” He had only to close his eyes, drop his thoughts inwards, sink after them himself, call aloud and—see.
His imagination conceived and bore—worlds; but nothing in these worlds became alive until he discovered its true and living name. The name was the breath of life; and, sooner or later, he invariably found it.
Once, having terrified his sister by affirming that a little man he had created would come through her window at night and weave a peaked cap for himself by pulling out all her hairs “that hadn’t gone to sleep with the rest of her body,” he took characteristic measures to protect her from the said depredations. He sat up the entire night on the lawn beneath her window to watch, believing firmly that what his imagination had made alive would come to pass.