Mozart wrote his music as if it were dictated to him by God. If you look at his sheet music (or just rent the movie Amadeus), you'll see that he never made any changes. Everything was exactly the way it was supposed to be the first time around. Mozart's genius was his incomparable talent.
Beethoven, on the other hand, would write a few notes. Look at them. Scratch a few of them out. Write a few more. Think about them. Change them. And change them again. If you look at his sheet music, you'll see a mess of scribbles, revisions, and second thoughts. Beethoven's genius was his indefatigable hard work.
I don't know about you, but I'm a Beethoven. I wholly subscribe to the adage "Hard work will be talent. Especially when talent doesn't work hard."