Both the expansion after the 2001 recession and the one after the Great Recession were strong in aggregate terms but unimpressive unless you were in a narrow slice at the top when you look at distribution; this is very different from the post-WWII expansion (even the 1980s and 1990s expansions were better distributionally than the later ones, though worse than earlier ones.)
The expansion that centered the Boomer experience and provides the experiential basis for the belief that effort is sufficient for success was different than anything Millennials (and even, to a lesser extent, Gen X) experienced.
In inflation adjusted terms, Millenials are far poorer than their parents for their phase in life on average. The latest number I can find is 20% less earnings than their parents at a comparable age.
Now Forbes argues that that’s because Millenials are extremely educated, their parents were working 4-8 longer than they were in their late 20s, giving Boomers more time to earn wealth.
While that’s certainly part of it, I don’t think it explains it all. The social contract around who gets the spoils of a growing economy seem to have shifted significantly since the 1980s. That an uneducated factory worker Boomer earned more in inflation adjusted money than a colleges educated Millenial indicates that something is up.