There is a world of difference between personal and merely subjective prayer. Prayer deserves to be called personal when it arises out of the dignity of man answering for himself, from the fountainhead of his inner life, and form the immediate encounter between him and his Creator and Redeemer. Prayer must be called subjective when the individual merely seeks himself, putting what seems true to him and his own uncertain religious sentiments in the place of revealed truth.
Romano Guardini, The Art of Praying, 1957.