A lot of the standard paths to success available to our parents - or even older gen-x cousins and siblings - weren't available. A lot of the assumptions about education and career needed to be abandoned. The boomer path of leaving college without crippling debt, and moving into a job right away where you stayed until you retired? Not really an option.
Had to figure out other ways of doing shit. Adapt and overcome - that is how the successful millennials did it, and a lot did. Cautious optimism in an unpredictable world describes it well.
All in all, though - wasn't even that tough to get a good partner and carve out a damn good life, with plenty of good earning years left.
Most of these Incels you are maligning look about the same age as my nephews - not sure they're millennials at all - but they might be fucked since the internet has made charm, wit, and cunning less of an asset in the dating world. Option paralysis. If I were young in this environment - don't know how I'd do since, as it has been pointed out to me, I come off like a dick online - which is where everyone meets now.