Is it because we don't want to see them succeed? Maybe. But in most cases it's because we want to be on an even keel with our mates. Especially if you're a power-mad egomaniac. I'm not saying I'm a power-mad egomaniac. I'm just saying if YOU were a power-mad egomaniac, it would probably steam you to see your friend get discovered by a casting agent and become a big movie star, like that kid from Harry Potter. Can you imagine what it would be like to be friends with him? He wouldn't have time for Taco Bell or basketball games anymore. He'd always be off doing a "press junket" or having dinner with Kirsten Dunst. (I've heard that all of Kirsten's old friends hate her because she's always flashing her cute belly--cute bellies are something to be modest about and not for flaunting in all your friend's faces.)
Now if you were friends with that singer guy from Papa Roach it might not be so bad. I mean, they're all stars and everything, but he's such a doughboy. Did you see that picture of him in Rolling Stone with his shirt off? Oh, it made me laugh. I mean, my stomach is not that pudgy. I think I could be friends with him.
The point is, we have to pick and choose our envies carefully. It's such a widely available state of mind these days. From those lazy afternoons watching torturous episodes of Cribs to listening to your friend tell you how happy their childhood was--it's everywhere to be had. All we can do is pace ourselves and decide who our true friends are.