The main idea of this book is that Rational Egoism is virtuous and necessary. We need to take accountability of our own future. When doing so, we improve the future for everybody. Out of egoism flows altruism. But the book packages and weaves this idea into a gripping story, where good and bad fight it out, and the egoistic people simply leave, letting society collapse and die. Hence the name of the book, Atlas Shrugged.
The main plot of the story revolves around a woman named Dagny Taggarty, who is running a railroad business. Because of her struggles the railroad keeps moving every day and on time, but she is on the point of breaking. Things are not going well.
There is tension. Cost-cutting and regulations creep in, which make the business harder to run each day. People pile up more and more constraints, but expect the same output from the railroad. The workload and requirements increase, but the people who expect results, don't want to do any work themselves. They want to use people like Dagny, to do their work for them, slowly binding and milking them for their own benefits, while relaxing themselves and gaining profits from the work of others.
In that process the book deals with the question of "Who is John Galt?" over and over again. In the book, this is a saying that expresses, "who cares?", thrown around when quality is lacking.
The answer to that question should be – us. We should be the ones who care. We should care to build quality. And be self-motivated and do our work. Not for the sake of others, but for the sheer happiness derived from the work and the products of the work. Building better machinery, uncovering the laws of the universe, and creation of beauty is rewarding. Doing science, engineering, writing, music and other things, helps to keep the world running. They are things we don't do for the sake of others, but for our own. The joy of creation, is what drives this work.
Because we want these things to exist in the real world, we go out and make them exist. We work very hard, to make them exist. That in a way is Ayn Rand's definition of virtue.When we are striving for our own good, to make our creations come true, that's when humans are virtuous. And in the process people improve the common good as well. Creation is making the pie bigger. It's not about dividing the pie, because that's a zero sum game. A finite game, not worth playing.
She contrasts it with another approach to life. That of controlling people and living of other people's work. Essentially figuring out ways to coerce and force people into doing your bidding. In a way, finding ways of dividing the pie instead of making it bigger. Always relying on others to actually create the pie, and then grabbing the biggest share of the pie, whenever possible.
Those are people, who for the sake of altruism, treat others, so that they don't have to take on responsibility for their own futures. To each according to their ability to each according to their needs, is their creed.
This ends up in a mess, and it's that mess that Atlas Shrugged shows in the form of a novel. When the people who work the hardest, gain nothing of their achievements, they might still work, because they love their work and creation so much. But it's fundamentally unfair to them. And if they, if only for a moment, "shrug" and stop working, the whole edifice of society comes crumbling down and desintegrates under it's own weight. Because if the people who work, had enough and stop, there wouldn't be anything anymore. And society would die.
The results of working and moving things, making things happen and materialize in the real world, is necessary for life. People who do this kind of work are what Ayn Rand calls "Prime Movers". They are the people who go out and make things happen. They are the people, who created the entire world as we know it today and who push progress. They are the John Galt's of this world.
In a way Ayn Rand tries to convince the readers to become Prime Movers themselves. Everybody, should be John Galt. Since the question to "who cares", should be, "us". We should care about quality and our own futures. We should be egoistic about it.