The Masked Beauty was his Wife

One of my all-time favourites in the history of philosophy is Schopenhauer's comment on Kant's moral philosophy:

I should liken Kant to a man at a ball, who all evening has been carrying on a love affair with a masked beauty in the vain hope of making a conquest, when at last she throws off her mask and reveals herself to be his wife.

The point being that Kant deluded himself into thinking that he was developing a rational basis for morality whilst expounding principles that mostly reflected his own Pietist upbringing and the maxims he adopted on his mother's knee.