Unless you're a cold-hearted monster who's completely dead on the inside, the ending of E.T. is a real sob fest. E.T.'s spaceship comes back for him, but before he can say, "Peace out, Earth," he must say goodbye to Gertie, Michael, and Elliott.
Of course, as Michael points out, E.T. doesn't know "goodbye," so everyone's favorite little squashy guy says farewell to each kid in the most appropriate way he can think of.
He tells Gertie to "Be good," which is one of the first things that she taught him to say. Callback! To Michael, E.T. says "Thank you." Michael says, "You're welcome." For a teenage boy, this is crazy-emotional. And then there's Elliott. E.T. asks Elliott to come with him. When Elliott says that he has to stay on Earth, E.T. touches his own heart and says, "Ouch." Another callback! Elliott tearfully does the same, and then hugs the heck out of E.T. while his family (and Keys) looks on.
But wait! It gets sadder! After they hug it out, E.T. holds his healing, glowing finger up to Elliott's forehead and says, "I'll be right here." Yet another callback! Then E.T. takes his pot of geraniums and leaves, presumably forever. Oof.
So what's up with all of the callbacks? That's easy. They're there to send your tear ducts into overdrive! The callbacks remind viewers of poignant moments earlier in the film—and if they were emotionally resonant the first time around, they're really going to pack an emotional punch here at the end of the film.
Elliott's refusal of E.T.'s offer to come with him is important, too, for the simple fact that it suggests that Elliott is growing up. One of the major themes of the film is youth (see our section on that for more). E.T. represents all of the best parts of being a kid, like discovery, wonder, and amazement. When E.T. leaves and Elliott stays, it suggests that Elliott's ready to take the confidence and wisdom that E.T. imparted and start becoming a young man.