Here’s a good quote:
At this point, don’t aspire to be great, or even to be original. Aspire to be prolific. That’s an aspiration you can control, and one that can lead — in less time than you might think — to greatness and originality.
That’s from Freehand Drawing & Discovery Urban Sketching and Concept Drawing for Designers by James Richards. It’s a highly-recommendable book on location sketching and much more.