Randy Pausch first delivered an actual speech, his "Last Lecture," when he left Carnegie Mellon University. He realized that the speech would be recorded, and he realized that he was therefore putting himself in a metaphorical "bottle that would one day wash up on the beach for [his] children."
Pausch's speech was so popular that he quickly turned it into a book as well. He was on a tight timeline for a heartbreaking reason: Randy had terminal pancreatic cancer.
Diagnosed with only months to live, Pausch set out to provide all the fatherly advice and wisdom which he would not live to personally provide to his children. He ends the actual lecture (which you can stream online) with the acknowledgement that the entire academic pretense of the lecture had been a "head fake": his intended audience was not in that room but existed in his young children who would grow up without their father.
The introduction of his book acknowledges the same idea. In this book, Pausch sets out to provide guidance to his children in how to deal with life's challenges (as he's been given a monumental one himself) and share with them some stories from his life that will help them live their own.
With such limited time remaining, Pausch carved out enough of it to provide fifty-three mini lectures in this book for his children's reference. He acknowledges that it's not a replacement for a living parent but that "engineering isn't about perfect solutions; it's about doing the best you can with limited resources."