Diderot could not deny himself a book or an engraving that struck his fancy, though he was quite willing to make a present of it to any appreciative admirer the day after he had bought it.

He was extravagant in hiring a hackney-coach where another person would have gone on foot, and not seldom the coachman stood for half a day at the door, while the heedless passenger was expatiating within upon truth, virtue, and the fine arts, unconscious of the passing hours and the swollen reckoning.

Hence, when the time came, there were no savings.

We have to take a man with the defects of his qualities, and as Diderot would not have been Diderot if he had taken time to save money, there is no more to be said.
When it became his duty to provide for his daughter, between 1763 and 1765, he resolved to sell his library.

Through Grimm, Diderot's position reached the ears of the Empress of Russia.