It’s a simple concept: A moth grows inside a cocoon. While it grows, it begins to dig a little hole in its cocoon so that when it’s strong enough, it can go out into the world. If someone were to help the moth get out of its cocoon before it was ready, it would die. Struggle is nature’s way of strengthening it.
The very wise John Locke applies this concept to Charlie’s drug addiction. When Charlie approaches Locke to ask for his heroin back, Locke tells him that he will only return it to him if he asks three times. Locke does this instead of just destroying the drugs, because if he did that he would be taking away Charlie’s choice, and life is all about choices.
A glimpse into Charlie’s past reveals that he was once just a music-loving church boy. But with the success of Drive Shaft came temptation: girls, drugs, etc. And though he fought off these temptations for longer than your average rock star, he couldn’t fight them off forever.
Charlie’s older brother, Liam, was key in Charlie’s transition from Church boy to heroin addict. He was also key in Charlie ending up on Flight 815, since Charlie was in Sydney to try to convince his now drug-free brother to return to Drive Shaft.
Back on the island, Jack has wound up pinned under a rock in one of the caves, unable to get out. Charlie volunteers to go in and save him, which then gives him the strength to make a very difficult decision.
While all of this is going on, Kate, Sayid and Boone plan to triangulate a signal so they can send a distress call. All goes as planned at first. But then just as all three rockets go off and Sayid begins to aquire a signal, someone knocks him out from behind and they are unable to make any contact.
At the end of the episode, Charlie goes to Locke for a third time and asks for his drugs.
Locke: This is the third time you’ve asked me. Are you sure you really want them?
Charlie: I’ve made my choice.
Locke hands over the drugs, and Charlie throws them into the fire.