The intro to my Quantum Mechanics textbook began with this:
And now, reader, bestir thyself. Though we will always lend thee proper assistance in difficult places, as we do not, like some others, expect thee to use the arts of divination to discover our meaning, yet we shall not indulge thy laziness where nothing but thy own attention is required; for thou art highly mistaken if thou dost imagine that we intended, when we began this great work, to leave thy sagacity nothing to do; or that, without sometimes exercising this talent, thou wilt be able to travel through our pages with any pleasure or profit to thyself."
That's an abridged quote from Henry Fielding, "The History of Tom Jones."
Or as close as I can remember it.