I now perceive one immense omission in my Psychology— the deepest principle of Human Nature is the craving to be appreciated, and I left it out altogether from the book, because I had never had it gratified till now.

William James (1842–1910) American psychologist and philosopher
Letter (1896-04-06) to his Philosophy 2A class, Radcliffe College, Cambridge, Massachusetts
    (Source)

The class had sent him a potted azalea at Easter.