McConaughey sat down with Fallon to promote his new children's book, Just Because, which just reached #1 on the NYT bestseller list. In case you were interested in what it's about, the pair give you an exciting preview of the book in the form of a rap.
McConaughey also revealed that he got the idea for the book in a dream.
"I never really thought about it. Look, this came to me in a little ditty of a dream one night, and I woke at 2:30 with this little, hook, you know," said the actor, 53. "Just because they threw the dart don't mean that it's stuck dun-dun-dun. Just because I got skills, don't mean there is no luck."
"And I woke, and it was a good dream, and as you do in good dreams when you don't want them to end, you try to keep the rhythm of the thought, right?" he continued.
"So I get up and I write all this stuff down. I write about 200 couplets, 30 of which made it into this version, 'cause this is a younger person version."
"And I looked at and I found those 30 I was like, 'Hey this is some stuff that my children are going through. This is some stuff that I hear my kids' friends talk about they're going through. This is some stuff that I hear parents that are friends of mine saying, 'my kids are going through this.' So, that's what's in the book."
McConaughey, who shared that his kids do like the book, also revealed that he isn't tired of saying, "alright, alright, alright," after all these years.
"People ask me all the time, 'Do you get tired of that?' I said, 'No, it's the first three words I ever said on film 32 years ago and it precedes me."
"I thought I might just have a one night hobby, it turned into a career. Please say it!"