Richard Hamming:

If you do not work on an important problem, it's unlikely you'll do important work.

From the archive:

Marge: I'd really like to give it a try!
Homer: I don't know, Marge, trying is the first step towards failure.

Also:

One passionate person is worth a thousand people who are just plodding along ...

Finally:

There are 260 million people in America, and you are one of them.