The final lesson he learned from his father was from how he died. His father died screaming in pain having a massive heart attack. The lesson Smith took from that was if that was his dad's reward for years of self-sacrifice and hating his job, than he might as well make as much a paradise for himself in this world as he could.
While that might sound like a sure fire recipe for self-indulgence, and maybe some can't see the difference between that and a life dedicated to self-expression, for Smith it provided the motivation for keeping as true to himself as possible. During the course of the book he describes what happened when he let his life drift off that path.
The worst of those experiences was directing Bruce Willis in Cop Out. While it earned him the respect of executives of the studio he did the film for, and led to more offers of directing work, he realized that even if he never had to work with a prima donna like Willis again, simply directing somebody else's material wasn't for him. It would eventually turn into a job he would hate, or at least resent, and that's not what he had set out to do when he embarked upon finding a way of making a living doing what he loved.
Smith is nothing if not honest. Throughout the entire book he's upfront with readers, telling them there's nothing easy about the course he's chosen and if they want to emulate what he's doing they're in for a hard slog. This is the tough shit of the title, "Security, normalcy, convenience, protection, and identity are opiates you've gotta wean yourself off before you can be an individual. You can't stand out if you're blending in."
Now that might sound easy but it has to be the hardest thing in the world to actually follow through on. He's talking about giving up everything from normal relationships to anything else you can think of that all of your friends will be doing.
Maybe that's why he's dedicated the book to such a specific part of his wife's anatomy. He goes into details for you in the chapter talking about her, but that's just his way of making the real point. Which is that he's been incredibly blessed not just because as he puts it "she's way out of my league" but because she willingly gave up her career as a journalist to join forces with him. That she allows him to be who he is warts and all and accepts that he won't change for anyone is a miracle and he knows it.