Issues of communication abound in The Lorax, and things get pretty ironic. Hipsters, watch out. The Lorax exists to speak for the forest creatures, creatures who can't speak with the Once-ler directly. But the Lorax and the Once-ler might as well have been speaking two different languages—the Lorax just can't break through to him. But here's the twist: the Once-ler really was listening, he just wasn't processing. He remembers every word the Lorax said, and now, as he tells his story to the boy, he finally understands the words. And bonus, he's able to communicate his understanding to the boy, who is listening pretty stinkin' attentively for a kid.
Q: Why does the Lorax yell all the time?
A: Maybe he needs an anger management class.
Q: Why does the Once-ler tell the boy his story?
A: Why not? (Just kidding—don't get your kid started.) Maybe the Once-ler thought the boy was a particularly good listener. Or maybe, just maybe, he told the boy his story because the boy asked. Curiosity doesn't always kill the cat.