Keats' speaker contemplates all of the things that he wants in life: namely, success, fame, and love. C'mon, is that too much to ask?
Well, as it turns out, the speaker is pretty sure that it is. See, he doesn't want just any old fame. He wants Fame. Capital letters and neon lights. (Okay – so they didn't have neon lights in the early 19th century, but you get our point.) He doesn't want just any old love, either. He wants that soul-stripping, earth-shaking, sky-tumbling once-in-a-lifetime sort of rapture. To sum it all up, he wants to be the star of pretty much every romantic movie ever.
Here's the problem: the speaker is also pretty sure that his life will end long before he'll be able to achieve any of these goals. That's why his description of his desires is so tinged with desperation – chances are, his life will be over far, far too quickly.
This poem charts both the speaker's desires and his despair (in that order). Come to think of it, the poem doesn't exactly end on a happy note. But hey, what's a good melodrama without a little tragedy?