Take a look at this great ad from Image Comics, one in a series featuring quotes from their creators. This one shows writer/artist Natalie Nourigat saying "There's always a better way to do things. You keep your eyes and ears open, never assume that you know it all, and you just keep improving."
At the individual level, each person is inspired to improve out of self-interest, but the accumulation of all those bits of self-interest translates into huge gains at the level of society. Of course, self-interest can refer to A) the desire to get a better income, or more praise, or ways to impress a mate, but also B) the innate desire to be better and challenge oneself.
Cynics will say that not everyone shares Natalie's work ethic. And they're right. There are certainly millions of people who are lazy. There are millions of people who don't like their jobs. There are millions of people who get along just fine doing what they're doing and don't feel motivated to challenge themselves. But I bet the proportion of people who are lazy or unmotivated is much smaller than our worst assumptions lead us to believe. Of course, there are also millions of people who don't have the time or energy or resources to go above and beyond because just getting by is exhausting.
But I don't think those people are a negative drain on society; rather, they're just sort of neutral. They're still contributing, but maybe not at Natalie's pace of productivity. The more important thing to realize is how few people are actively trying to be worse at their jobs - surely a small number. If the vast majority of people are either eagerly pushing forward or neutral, civilization in aggregate moves forward. This is why productivity keeps increasing and rarely regresses. So, not everyone needs to work quite as hard as Natalie.
This work ethic has always existed, but progress is happening much faster nowadays due to improved communications technology and information storage. Because of it, Natalie can easily share what she learns and inspire others. In fact, she does this, posting on her blog guides, sketches, updates, and even samples of influences. Did you know YouTube is filled with artists who have recorded themselves working as videos so others can watch and learn from the process? (Like this great one from Sara Pichelli.) Other artists post step-by-step tutorials as well, such as this one by Kat Laurange.
When I was in school for art, we didn't have any of this. (Not to mention Meetups, such as the Central Park Sketch Meetup, of course.) It is so much easier for a novice to get started with art nowadays, and get free training. Some of them will turn into great artists, whereas in the past they would never had had the opportunity (only a select few people ever got into drawing schools or got to be an artist's apprentice).
It's only a small percentage of people that need to be instructing or pushing the envelope at any given time, but that knowledge adds up faster since it's now all easily available. Anything Natalie learns - which pen works best, how to compose a page, how to schedule her day - she passes along and other people can pick up. And of course, bad information gets shared as well, but the cream eventually always rises to the top. Now think about how that's true in every field, not just art. Anyone innovating and teaching helps to drag all the rest of us along, constantly building a smarter, more advanced civilization.