All you learn and all you can read will be of little use to you if you do not think and reason upon it yourself. One reads to know other people’s thoughts, but if we take them upon trust, without examining and comparing them with our own, it is really living upon other people’s scraps or retailing other people’s goods. To know the thoughts of others, is of use, because it suggests thoughts to one’s self, and helps one
to form a judgment; but to repeat other people’s thoughts, without considering whether they are right or wrong, is the talent only of a parrot, or at most a player.

Lord Chesterfield (1694-1773) English statesman, wit [Philip Dormer Stanhope]

Letter to his son, #67, “Thursday” (1740-41)
    (Source)