The invisible hand is an imaginary force, invented (arguably 'discovered') by Adam Smith, to explain the way that markets, composed of selfish desires, can have non-selfish consequences.
It is a classic case of "emergence", where a thing of one type leads to a thing of an entirely different type, when viewed at a different scale.
Economists and libertarians love this invisible hand business, but not nearly as much as the rich love this little theory. They also have all the power and influence, so they can happily publish and distribute this theory in all of their publications.
Whenever there are "externalities"—where the actions of an individual have impacts on others for which they do not pay, or for which they are not compensated—markets will not work well.