The elaboration on this bit is good:

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"[C]onsider two indistinguishable workers, you and your clone. By definition, you/clone have the same gender, ethnicity, years of schooling, family background, skills, etc. In 2006 you/clone graduated with identical academic records from the same university and obtained identical job offers from Facebook and MySpace. Not knowing any more about the future than the analysts who valued Facebook and MySpace roughly equally in the mid-2000s, you/clone flipped coins to decide which offer to accept: heads – Facebook; tails – MySpace. Clone’s coin came up heads. Yours came up tails. Ten years later, Clone is in the catbird’s seat in the job market — high pay, stock options, a secure future. You struggle. Back to university? Send job search letters to close friends? Ask distant acquaintances to help? The you/clone thought experiment may seem extreme, but recent research that I have conducted with colleagues finds that the earnings of workers with near-clone similarity in attributes diverged so much by the place they worked that rising inequality in pay among employers has become the major factor in the trend rise in inequality. ... The labor market has been dominated by economic forces that pull the wages of firms further apart from each other, motivating our analysis of the role of employers in increasing inequality."